Removed broken use of Stdio.is_file(path)
Stdio.is_file(path) should not be used to check if some path is a
file, because it is not whether path is a file or not in the working
tree which is relevant, but rather whether or not it is one in the
commit/stage being investigated. In fact, there might not even be
a working tree since this test is also run on the server.
Instead, use get_file(path,2), which returns the empty string for
directories, which should have the intended effect of not complaining
about foreign_ident being removed from directories.