The uninitialized variable seems harmless in practice, but let's still be clean.

Implement a gate between git and mediawiki, allowing git users to push
and pull objects from mediawiki just as one would do with a classic git
repository thanks to remote-helpers.

Currently supported commands are :

     git clone mediawiki::http://onewiki.com
     git pull

The following packages need to be installed (available on common
repositories):

     libmediawiki-api-perl
     libdatetime-format-iso8601-perl

Use remote helpers in order to be as transparent as possible to the git
user.

Download Mediawiki revisions through the Mediawiki API and then
fast-import into git.

Mediawiki revisions and git commits are linked thanks to notes bound to
commits.

The import part is done on a refs/mediawiki/<remote> branch before
coming to refs/remote/origin/master (Huge thanks to Jonathan Nieder
for his help)

We were not able to reproduce the empty timestamp bug noticed by Jeff
King, thus needing some further testing. A placeholder is still
implemented just in case. Its value is the value of the last valid
timestamp received + 1.

With "use encoding 'utf-8'" non-iso characters are now fully supported
in both file content and filename.
A small helper run_git is also added to execute any git command, helping
to also utf-8 encode results from git commands.
However, utf-8 encoding for filenames could raise problems if different
file systems handle utf-8 filenames differently. A uri_escape of
mediawiki filenames could be imaginable, and is still to be discussed
further.

Partial cloning is supported using the following syntax:
"git clone mediawiki::http://wikiurl##A_Page##Another_Page"
As always, this url is kept in .git/config, helping to always keep
track of these specific pages

Signed-off-by: Jérémie Nikaes <jeremie.nikaes@ensimag.imag.fr>
Signed-off-by: Arnaud Lacurie <arnaud.lacurie@ensimag.imag.fr>
Signed-off-by: Claire Fousse <claire.fousse@ensimag.imag.fr>
Signed-off-by: David Amouyal <david.amouyal@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Sylvain Boulmé <sylvain.boulme@imag.fr>

Push is now supported by the remote-helper
Thanks to notes metadata, it is possible to compare remote and local
last mediawiki revision to warn non fast-forward and everything
up-to-date.

When allowed, push looks for each commit between remotes/origin/master
and HEAD, catches every blob related to these commit and push them in
chronological order. To do so, it uses git rev-list --children HEAD and
travels the tree from remotes/origin/master to HEAD through children. In
other words :

	* Shortest path from remotes/origin/master to HEAD
	* For each commit encountered, push blobs related to this commit

An automatic git pull --rebase is executed after a successful push to
get metadata back from mediawiki. This is also done to maintain
closeness with the form of a mediawiki history. It can be a problem
since it also flatens the entire history. (This solution is still
to be discussed).

To send files to mediawiki, the mediawiki API is used. A filter is
applied to the data send because mediawiki pages cannot have blank
characters at the end. The filter is thus more or less a right trim.

Signed-off-by: Jérémie Nikaes <jeremie.nikaes@ensimag.imag.fr>
Signed-off-by: Arnaud Lacurie <arnaud.lacurie@ensimag.imag.fr>
Signed-off-by: Claire Fousse <claire.fousse@ensimag.imag.fr>
Signed-off-by: David Amouyal <david.amouyal@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Sylvain Boulmé <sylvain.boulme@imag.fr>