The xdl_prepare_env() function may initialise an xdlclassifier_t
data structure via xdl_init_classifier(), which allocates memory
to several fields, for example 'rchash', 'rcrecs' and 'ncha'.
If this function later exits due to the failure of xdl_optimize_ctxs(),
then this xdlclassifier_t structure, and the memory allocated to it,
is not cleaned up.

In order to fix the memory leak, insert a call to xdl_free_classifier()
before returning.

This patch was originally written by Ramsay Jones (see commit
87f16258367a3b9a62663b11f898a4a6f3c19d31 in git.git).

Commit 307ab20b3 ("xdiff: PATIENCE/HISTOGRAM are not independent option
bits", 19-02-2012) introduced the XDF_DIFF_ALG() macro to access the
flag bits used to represent the diff algorithm requested. In addition,
code which had used explicit manipulation of the flag bits was changed
to use the macros.

However, one example of direct manipulation remains. Update this code to
use the XDF_DIFF_ALG() macro.

This patch was originally written by Ramsay Jones (see commit
5cd6978a9cfef58de061a9525f3678ade479564d in git.git).

This special-casing ignores that we might have a locked file, so the
hashtable does not represent the contents of the file we want to
write. This causes multivar writes to overwrite entries instead of add
to them when under lock.

There is no need for this as the normal code-path will write to the file
just fine, so simply get rid of it.

The function to extract signatures suffers from a similar bug to the
header field finding one by having an unecessary line feed check as a
break condition of its loop.

Fix that and add a test for this single-line signature situation.

While often similar, these are not the same on Windows. We want to use the page
size on Windows for the pools, but for mmap we need to use the allocation
granularity as the alignment.

On the other platforms these values remain the same.

This is especially useful in combination with MinGW to yield the
Windows-compliant DLL name "git2.dll" instead of "libgit2.dll"

This is useful to force "smart" IDEs (like CLIon) to use debug
flag -g even it may have decided that "-D_DEBUG" (which is
already present) is sufficient.

This ensures that when using OpenSSL a safe default set of ciphers
is selected. This is done so that the client communicates securely
and we don't accidentally enable unsafe ciphers like RC4, or even
worse some old export ciphers.

Implements the first part of https://github.com/libgit2/libgit2/issues/3682

Callers of `git_config__cvar` already handle the case where the
function returns an error due to a failed configuration variable
lookup, but we are actually swallowing errors when calling
`git_config__lookup_entry` inside of the function.

Fix this by returning early when `git_config__lookup_entry`
returns an error. As we call `git_config__lookup_entry` with
`no_errors == false` which leads us to call `get_entry` with
`GET_NO_MISSING` we will not return early when the lookup fails
due to a missing entry. Like this we are still able to set the
default value of the cvar and exit successfully.

When writing to a file with locking not check if writing the
locked file actually succeeds. Fix the issue by returning error
code and message when writing fails.

When normalizing options we try to look up HEAD's OID. While this
action may fail in malformed repositories we never check the
return value of the function.

Fix the issue by converting `normalize_options` to actually
return an error and handle the error in `git_blame_file`.

We usually check entries returned by `git_sortedcache_entry` for
NULL pointers. As we have a write lock in `packed_write`, though,
it really should not happen that the function returns NULL.

Assert that ref is not NULL to silence a Coverity warning.

Curl by default does not report errors by setting the error code.
As the upload can fail through several conditions (e.g. the rate
limit, leading to unauthorized access) we should indicate this
information in Travis CI.

To improve upon the behavior, use `--write-out=%{http_code}` to
write out the HTTP code in addition to the received body and
return an error if the code does not equal 201.

When the user passes in a diff which has no repository associated
we may call `git_config__get_int_force` with a NULL-pointer
configuration. Even though `git_config__get_int_force` is
designed to swallow errors, it is not intended to be called with
a NULL pointer configuration.

Fix the issue by only calling `git_config__get_int_force` only
when configuration could be retrieved from the repository.

In C89 it is undefined behavior to pass `NULL` pointers to
`strncmp` and later on in C99 it has been explicitly stated that
functions with an argument declared as `size_t nmemb` specifying
the array length shall always have valid parameters, no matter if
`nmemb` is 0 or not (see ISO 9899 §7.21.1.2).

The function `str_equal_no_trailing_slash` always passes its
parameters to `strncmp` if their lengths match. This means if one
parameter is `NULL` and the other one either `NULL` or a string
with length 0 we will pass the pointers to `strncmp` and cause
undefined behavior.

Fix this by explicitly handling the case when both lengths are 0.

When computing a short OID we do this by first copying the
leading parts into the new OID structure and then setting the
trailing part to zero. In the case of the desired length being
`GIT_OID_HEXSZ - 1` we will call `memset` with an out of bounds
pointer and a length of 0. While this seems to cause no problems
for common platforms the C89 standard does not explicitly state
that calling `memset` with an out of bounds pointer and
length of 0 is valid.

Fix the potential issue by using the newly introduced
`git_oid__cpy_prefix` function.

This fixes an issue in Xcode 7.3 in objective-git where we get the error
"Include of non-modular header file in module". Not importing this
header again fixes the issue.

When parsing a section header we expect something along the
format of '[section "subsection"]'. When a section is
mal-formated and is entirely missing its quotation marks we catch
this case by observing that `strchr(line, '"') - strrchr(line,
'"') = NULL - NULL = 0` and error out. Unfortunately, the error
message is misleading though, as we state that we are missing the
closing quotation mark while we in fact miss both quotation
marks.

Improve the error message by explicitly checking if the first
quotation mark could be found and, if not, stating that quotation
marks are completely missing.

The first time may be due to memory fragmentation or just bad luck on a
32-bit system. When we hit the mmap error for the first time, free up
the unused windows and try again.

When looking up an abbreviated oid, show the actual (abbreviated) oid
the caller passed instead of a full (but ambiguously truncated) oid.

The inner packet may be split across multiple sideband packets.

ssh, ssh+git and git+ssh should all successfully build an SSH transport

Also moving var declarations to top of blocks to support bad old compilers

The parser now also supports digits, '-' and '.'. https://github.com/nodejs/http-parser/pull/276