Fixing Git commit, as far as it should work as git commit -a.

In order to maintain the same behavior between mercurial and git, the commit should do a "git commit -a" but it was not.

I thought in implement it as optional, but mercurial does not have an index, so I've had to implement one for it and I think it is too much work right now.

So, now it works as documentation said it should.
I think this is different to what mercurial does, mercurial needs to remove a file with "hg rm" to commit its removal. So it seems that to mimic mercurial behaviour we'd have to check for `GIT_STATUS_INDEX_DELETED`, but as it'd be already staged I guess these two lines are not needed.