Patches for libgit2

Hi,

Please find patches for libgit2. They allowed me to read the history of a
repository with only 75 patches but hacked by an history shortening.

Commits were both in a 5 GB pack file and loose objects. So I had to add
support for pack files. Hopefully, reading idx files was already there so I
followed the same model.

Patches can also be cloned at "git://git.hforge.org/libgit2.git".

There is a Python wrapper on the next side, forking from the existing
libgit2-python [1]. They bring the same functionnalities but the patches are
not slick yet.

[1] http://code.istique.net/gitweb/?p=libgit2-python.git;a=summary

One thing that would miss is unit tests, but I lack experience on testing C
code, and it would require having a small but exhaustive pack file with
different types of object, including ofs and ref deltas. Help on this part is
welcome.

Next step would be decoding raw objects to commits, trees, blobs and tags.
There is already the start of a commit structure. I'll be starting from that.

Regards,

Hervé