Weird git_status_file() behavior

This mainly relates to git-tfs/git-tfs#231 issue.

The test has been written in C# and is available in the [libgit2sharp/status-and-ignore-casing](https://github.com/libgit2/libgit2sharp/tree/test/status-and-ignore-casing) branch.

In order to ease the troubleshooting, it's now ported in C and still fails