Merge branch 'js/bs-is-a-dir-sep-on-windows'

Merge branch 'js/bs-is-a-dir-sep-on-windows'

"foo\bar\baz" in "git fetch foo\bar\baz", even though there is no
slashes in it, cannot be a nickname for a remote on Windows, as
that is likely to be a pathname on a local filesystem.

* js/bs-is-a-dir-sep-on-windows:
  Windows: do not treat a path with backslashes as a remote's nick name
  mingw.h: permit arguments with side effects for is_dir_sep