This update addresses all of the feedback in pull request #570.

The biggest change was to create actual linked list stacks for
storing the tree and workdir iterator state.  This cleaned up
the code a ton.  Additionally, all of the static functions had
their 'git_' prefix removed, and a lot of other unnecessary
changes were removed from the original patch.

This makes two changes to iterator behavior: first, advance
can optionally do the work of returning the new current value.
This is such a common pattern that it really cleans up usage.

Second, for workdir iterators, this removes automatically
iterating into directories.  That seemed like a good idea,
but when an entirely new directory hierarchy is introduced
into the workdir, there is no reason to iterate into it if
there are no corresponding entries in the tree/index that it
is being compared to.

This second change actually wasn't a lot of code because not
descending into directories was already the behavior for
ignored directories.  This just extends that to all directories.

This create a new git_iterator type of object that provides a
uniform interface for iterating over the index, an arbitrary
tree, or the working directory of a repository.

As part of this, git ignore support was extended to support
push and pop of directory-based ignore files as the working
directory is being traversed (so the array of ignores does
not have to be recreated at each directory during traveral).

There are a number of other small utility functions in buffer,
path, vector, and fileops that are included in this patch
that made the iterator implementation cleaner.

Fix copy-paste error

Remotes improvements

Allow setting the fetch and push refspecs, which is useful for
creating new refspecs.

notes: fix assert

Hopefully fix issue "Don't sleep and code" - #558.

Signed-off-by: schu <schu-github@schulog.org>

Notes API

This commit adds basic git notes support to libgit2, namely:

* git_note_read
* git_note_message
* git_note_oid
* git_note_create
* git_note_remove

In the long run, we probably want to provide some convenience callback
mechanism for merging and moving (filter-branch) notes.

Signed-off-by: schu <schu-github@schulog.org>

This is legacy compat stuff for when `deflateBound` is not defined, but
we're not embedding zlib and that function is always available. Kill
that with fire.

git__ishex allows to check if a string is a hexadecimal representation.

Signed-off-by: schu <schu-github@schulog.org>

git_commit_create is supposed to update the given reference
"update_ref", but segfaulted in case of a yet to be born
reference. Fix it.

Signed-off-by: schu <schu-github@schulog.org>

Update Copyright header

Signed-off-by: schu <schu-github@schulog.org>

Fix "clang warning: expression result unused"

tests-clar: fix warning sign-compare

Signed-off-by: schu <schu-github@schulog.org>

revwalk: unmark commits as uninteresting on reset

Not doing so hides commits we want to get at during a second walk.

Add libgit2-glib link to README.md

This lovely and much delayed release of libgit2 ships from the cold city
of Brussels, which is currently hosting FOSDEM 2012.

There's been plenty of changes since the latest stable release, here's a
full summary:

- Git Attributes support (see git2/attr.h)
	There is now support to efficiently parse and retrieve information
	from `.gitattribute` files in a repository. Note that this
	information is not yet used e.g. when checking out files.

- .gitignore support
	Likewise, all the operations that are affected by `.gitignore` files
	now take into account the global, user and local ignores when
	skipping the relevant files.

- Cleanup of the object ownership semantics
	The ownership semantics for all repository subparts (index, odb,
	config files, etc) has been redesigned. All these objects are now
	reference counted, and can be hot-swapped in the middle of
	execution, allowing for instance to add a working directory and an
	index to a repository that was previously opened as bare, or to
	change the source of the ODB objects after initialization.

	Consequently, the repository API has been simplified to remove all
	the `_openX` calls that allowed setting these subparts *before*
	initialization.

- git_index_read_tree()
	Git trees can now be read into the index.

- More reflog functionality
	The reference log has been optimized, and new API calls to rename
	and delete the logs for a reference have been added.

- Rewrite of the References code with explicit ownership semantics
	The references code has been mostly rewritten to take into account
	the cases where another Git application was modifying a repository's
	references while the Library was running.

	References are now explicitly loaded and free'd by the user, and
	they may be reloaded in the middle of execution if the user suspects
	that their values may have changed on disk. Despite the new
	ownership semantics, the references API stays the same.

- Simplified the Remotes API
	Some of the more complex Remote calls have been refactored into
	higher level ones, to facilitate the usual `fetch` workflow of a
	repository.

- Greatly improved thread-safety
	The library no longer has race conditions when loading objects from
	the same ODB and different threads at the same time. There's now
	full TLS support, even for error codes. When the library is built
	with `THREADSAFE=1`, the threading support must be globally
	initialized before it can be used (see `git_threads_init()`)

- Tree walking API
	A new API can recursively traverse trees and subtrees issuing callbacks for
	every single entry.

- Tree diff API
	There is basic support for diff'ing an index against two trees.

- Improved windows support
	The Library is now codepage aware under Windows32: new API calls
	allow the user to set the default codepage for the OS in order to
	avoid strange Unicode errors.

treebuilder: remove needless variable entry_count

Signed-off-by: schu <schu-github@schulog.org>

Fix trailing slash issue to the gitdir path when the repo is opened through a workdir

repository: ensure that the path to the .git directory ends with a forward slash when opening a repository through a working directory path

This fixes an issue which was detected while using one of the libgit2 bindings [0]. The lack of the trailing forward slash led the name of references returned by git_reference_listall() to be prefixed with a forward slash.

  [0]: https://github.com/libgit2/libgit2sharp/pull/108

Fix the build on Emscripten

struct timeval is used in this file, which requires <sys/time.h> to be
included.

On non-Windows builds, we will now use _GNU_SOURCE so header
files will include modern API extensions.  This should resolve
issue #547.

Add unit tests to confirm ignore directory pattern matches and
to confirm that ignore and attribute files are loaded properly
into the attribute file cache.

Actually look for the file by the same cache key that we
store it under.  Rocket science!