If there exists a conflict in the index, but no file in the working
directory, this implies that the user wants to accept the resolution
by removing the file.  Thus, remove the conflict entry from the
index, instead of trying to add a (nonexistent) file.

Mark the `old_file` and `new_file` sides of a delta with a new bit,
`GIT_DIFF_FLAG_EXISTS`, that introduces that a particular side of
the delta exists in the diff.

This is useful for indicating whether a working directory item exists
or not, in the presence of a conflict.  Diff users may have previously
used DELETED to determine this information.

When confronted with a conflict in the index, `git_index_add_all`
should stage the working directory copy.  If there is no file in the
working directory, the conflict should simply be removed.

cl_git_sandbox_init_new() will create a clar temp directory and
initialize a new repository at that location.

It's not always obvious the mapping between stage level and
conflict-ness.  More importantly, this can lead otherwise sane
people to write constructs like `if (!git_index_entry_stage(entry))`,
which (while technically correct) is unreadable.

Provide a nice method to help avoid such messy thinking.

Since a diff entry only concerns a single entry, zero the information
for the index side of a conflict.  (The index entry would otherwise
erroneously include the lowest-stage index entry - generally the
ancestor of a conflict.)

Test that during status, the index side of the conflict is empty.

Make sure that we provide a blanked nitem side when the item does not
exist in the working directory.

When diffing against an index, return a new `GIT_DELTA_CONFLICTED`
delta type for items that are conflicted.  For a single file path,
only one delta will be produced (despite the fact that there are
multiple entries in the index).

Index iterators now have the (optional) ability to return conflicts
in the index.  Prior to this change, they would be omitted, and callers
(like diff) would omit conflicted index entries entirely.

If `git_index_remove_bypath` does no work, and returns an OK error
code, it should not set an error message.

When adding a conflict for some path, remove the staged entry.
Otherwise, an illegal index (with both stage 0 and high-stage
entries) would result.

Wrap the iterator current / advance functions so that we can extend
them, but also handle GIT_ITEROVER cases in the iterator funcs
instead of the callers.

Fix ident replacement to match Git behavior

Git inserts a space after the SHA1 (as of 2.1.4 at least), so do the
same.

Thin packs: don't 

When thickening a pack, avoid loading already loaded bases and
trying to insert them all over again.

When creating an index, know that we do not have an index for
our own packfile, preventing some unnecessary file opens and
error reporting.

openssl: don't try to handle WANT_READ or WANT_WRITE

Fix error when building as C++.

index_add_all: include untracked files in new subdirs

No need to get reports about individual ignored files, having a
single ignored directory delta is enough.

ignore: clear the error when matching a pattern negation

When we discover that we want to keep a negative rule, make sure to
clear the error variable, as it we otherwise return whatever was left by
the previous loop iteration.

Our doc parser really wants the types to be declared in the header it's
reading.

Improve server error reporting

This can be used by tools to show mesages about failing to communicate
with the server. The error message in this case will often contain the
server's error message, as far as it managed to send anything.

When we fail to read from stdout, it's typically because the URL was
wrong and the server process has sent some output over its stderr
output.

Read that output and set the error message to whatever we read from it.

Use a diff for iteration in index_update_all and index_add_all

Provide error messages for git_path_direach operations

We set an error if we get an error when reading, but we don't bother
setting an error message for write failing. This causes a cryptic error
to be shown to the user when the target filesystem is full.