Change the name of the .git directory.

[schwern]

Very rarely a release will ship with a .git directory. This interferes with our .git directory. Right now we just delete it. See #78.

A better way would be to use the GIT_DIR environment variable, or similar, to change the location of the git repository, perhaps even outside the working directory.

[schwern]

Git::Raw does not appear to be honoring the GIT_DIR env variable and I can't find a way to change where it looks for the .git directory.