Handle `git_path_diriter` instances at the drive root on Windows

iterator: loop fs_iterator advance (don't recurse)

The canonical directory path of the root directory of a volume on
POSIX already ends in a slash (eg, `/`).  This is true only at the
root.  Do not add a slash to paths in this case.

The canonical directory path of the root directory of a volume on
windows already ends in a slash (eg, `c:/`).  This is true only
at the volume root.  Do not add a slash to paths in this case.

Ensure that we can iterate the filesystem root and that paths come
back well-formed, not with an additional '/'.  (eg, when iterating
`c:/`, expect that we do not get some path like `c://autoexec.bat`).

push: put the git_oid inline in the test structure

iterator: advance the tree iterator smartly

Don't free config in `git_transaction_commit`.

The config is not owned by the transaction, so please don’t free it.

The previous commit left the comment referencing the earlier state of
the code, change it to explain the current logic. While here, change the
logic to avoid repeating the copy of the base pattern.

submodule: refactor to be more explicit in the search

These are small pieces of data, so there is no advantage to allocating
them separately. Include the two ids inline in the struct we use to
check that the expected and actual ids match.

diff: examine pathlist on non-files

When we're not doing pathspec matching, we let the iterator handle
file matching for us.  However, we can only trust the iterator to
return *files* that match the pattern, because the iterator must
return directories that are not strictly in the pathlist, but that
are the parents of files that match the pattern, so that diff can
later recurse into them.

Thus, diff must examine non-files explicitly before including them
in the delta list.

Ensure that a diff with the workdir is not erroneously returning
directories.

Mempack fix

It calls git_mempack_reset which reallocates the object array. git_oidmap_free is now called on it explicitly.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

Error: stack overflow.

git_mempack_reset was leaving free'd pointers in the oidmap.

When searching for information about a submdoule, let's be more explicit
in what we expect to find. We currently insert a submodule into the map
and change certain parameters when the config callback gets called.

Switch to asking for the configuration we're interested in, rather than
taking it in an arbitrary order.

report libssh2 error if list of authentication methods can't be retrieved

filebuf: ensure we can lock a hidden file

Revert "Get rid of libssh2 embedding"

index: canonicalize directory case when adding

New feature: add the ablility to iterate through a directory in index

On case insensitive platforms, allow `git_index_add` to provide a new
path for an existing index entry.  Previously, we would maintain the
case in an index entry without the ability to change it (except by
removing an entry and re-adding it.)

Higher-level functions (like `git_index_add_bypath` and
`git_index_add_frombuffers`) continue to keep the old path for easier
usage.

On case insensitive systems, when given a user-provided path in the
higher-level index addition functions (eg `git_index_add_bypath` /
`git_index_add_frombuffer`), examine the index to try to match the
given path to an existing directory.

Various mechanisms can cause the on-disk representation of a folder
to not match the representation in HEAD or the index - for example,
a case changing rename of some file `a/file.txt` to `A/file.txt`
will update the paths in the index, but not rename the folder on
disk.

If a user subsequently adds `a/other.txt`, then this should be stored
in the index as `A/other.txt`.

filebuf: follow symlinks when creating a lock file

Use a hashmap for path-based lookups in the index

We create a lockfile to update files under GIT_DIR. Sometimes these
files are actually located elsewhere and a symlink takes their place. In
that case we should lock and update the file at its final location
rather than overwrite the symlink.

Find the first index entry matching a prefix.

This should let us see more clearly what we're doing and avoid the ugly
'if' we need every time we want to interact with the map.

The embedding was removed as a libssh2 release with Windows crypto
support became available, but dependencies are still annoying so this
ahs been requested again.

This reverts commit 20dcb731.