git_clone now produces a repo that 
`git status` reports as clean!

Properly handling file modes. Still needs line-
ending transformations.

Now creating a local branch that tracks to the
origin's HEAD branch, and setting HEAD to that.

Also standardized on 3-space indentation. Sorry
about that.

So far they only create a repo, setup the "origin"
remote, and fetch. The API probably needs work as
well; there's no way to get progress information
at this point.

Also uncovered a shortcoming; git_remote_download
doesn't fetch over local transport.

The second call to assert_config_entry_on_init_bytype is cleaned up by
the main cleanup function, but that overwrites the first _repo. Make
sure that one doesn't leak.

The call to repo_init_reinit already takes care of opening the
repository and giving us a git_repository object to give to the
caller. There is no need to call git_repository_open again.

Fix Makefile.emebed for mingw32

Don't need unix/*.c for windows, don't need wildcard for regex.c

Revparse fixup

otherwise we can't compile the native parts of the rugged gem on Windows

When the creation of one iterator fails, we need to free the prefix
and possibly one of the iterators. Make sure we do so.

If we find several objects with the same prefix, we need to free the
memory where we stored the earlier object. Keep track of the raw.data
pointer across read_prefix calls and free it if we find another
object.

Make index add/append support core.filemode flag

message: Expose git_message_prettify()

oid_for_tree_path may not always find the path in the tree, in which
case we need to return an error. The current code doesn't do this and
results in undefined behavior.

This fixes git_index_add and git_index_append to behave more like
core git, preserving old filemode data in the index when adding
and/or appending with core.filemode = false.

This also has placeholder support for core.symlinks and
core.ignorecase, but those flags are not implemented (well,
symlinks has partial support for preserving mode information in
the same way that git does, but it isn't tested).

Fix potential segfault in revparse.