Merge branch 'js/gitdir-at-unc-root'

On Windows, the root level of UNC share is now allowed to be used
just like any other directory.

* js/gitdir-at-unc-root:
setup_git_directory(): handle UNC root paths correctly
Fix .git/ discovery at the root of UNC shares
setup_git_directory(): handle UNC paths correctly

diff --cc setup.c
Simple merge