This simplifies git_path_is_empty_dir on both Windows (getting rid
of git_buf allocation inside the function) and other platforms (by
just using git_path_direach), and adds tests for the function, and
uses the function to simplify some existing tests.

In email, Torsten Bögershausen agreed that we could use his code
from core Git in libgit2 under the modified license.  Also, since
his work is the basis for much of the precompose unicode support,
I have added him to the AUTHORS file as well.

This hooks up git_path_direach and git_path_dirload so that they
will take a flag indicating if directory entry names should be
tested and converted from decomposed unicode to precomposed form.
This code will only come into play on the Apple platform and even
then, only when certain types of filesystems are used.

This involved adding a flag to these functions which involved
changing a lot of places in the code.

This was an opportunity to do a bit of code cleanup here and there,
for example, getting rid of the git_futils_cleanupdir_r function in
favor of a simple flag to git_futils_rmdir_r to not remove the top
level entry.  That ended up adding depth tracking during rmdir_r
which led to a safety check for infinite directory recursion.  Yay.

This hasn't actually been tested on the Mac filesystems where the
issue occurs.  I still need to get test environment for that.

This doesn't actual do string precompose but it puts the hooks in
place into the iterators and the git_path_dirload function so that
the actual precompose work is ready to go.

This adds initialization of core.precomposeunicode to repo init
on Mac.  This is necessary because when a Mac accesses a repo on
a VFAT or SAMBA file system, it will return directory entries in
decomposed unicode even if the filesystem entry is precomposed.

This also removes caching of a number of repo properties from the
repo init pipeline because these are properties of the specific
filesystem on which the repo is created, not of the system as a
whole.

network cancellation improvements

commit: Introduce git_commit_message_raw()

HTTP: handle "relative" redirects

This commit adds cancellation for the push operation. This work consists of:

1) Support cancellation during push operation
    - During object counting phase
    - During network transfer phase
        - Propagate GIT_EUSER error code out to caller
2) Improve cancellation support during fetch
    - Handle cancellation request during network transfer phase
    - Clear error string when cancelled during indexing
3) Fix error handling in git_smart__download_pack

Cancellation during push is still only handled in the pack building and
network transfer stages of push (and not during packbuilding).

An alternative for 'clone' with options

There's no need for this to be a pointer to somewhere else.

Hopefully clear up what they're for.

Make the difference more explicit.

This wasremoved as part of the large culling a few commits ago.

This is a small thing that by itself doesn't quite justify making the
user use clone_into.

The removal of many options which lead to the direct usage of the
user's checkout options means we should make sure they remain const.

This used to be done via transport flags, which was removed in a
previous commit.

The basic clone function is there to make it easy to create a "normal"
clone. Remove a bunch of options that are about changing the remote's
configuration.

Unify the code bases.

Downloading all tags is part of what makes it a clone instead of
simply a fetch.

This allows you to set up the repository and remote as you which to
have them before performing the clone operation.

Move this one as well, letting us have a single way of setting the
callbacks for the remote, and removing fields from the clone options.

The text progress and update_tips callbacks are already part of the
struct, which was meant to unify the callback setup, but the download
one was left out.

Add git_transport_register, git_transport_unregister

Config subsection name should allow to have ']' and '\\' should allow to escape any characters

Redir refactor

Initial Implementation of progress reports during push

Never consider submodules for stashing

...before the helper's cleanup method tries to delete their files.

Fix x86/x64 size_t related warnings