[Bug] Unexpected behavior on case insensitive filesystems

[Alex Brachet-Mialot]

Branches behave weirdly for case insensitive filesystems, and I'm
guessing other things as well. For example say I am on a branch other
than master, checking out 'Master' will _work_, I will of course be on
the right branch but git status will say I am on 'Master' (expected
just 'master') and git branch will highlight no branch.