add index (git_merge_result struct has a pointer to index)
Fix wrap_index.
add merge_commits
bump pygit2
fix test_blame
add test, restore merge_result
Fix again.
fix test
Merge pull request #26 from huanghuang/pygit2:index

add index (git_merge_result struct has a pointer to index)
bump libgit2 for merge submodule
change pygit2 to use bumped libgit2
Merge pull request #27 from huanghuang/pygit2:bump

bump libgit2 for merge_commits support submodule
Fix bump.
Fix.
Merge pull request #28 from xutao/pygit2:fix

Fix bump.
Merge remote-tracking branch 'origin/master' into gh_douban