Fix problem when changing a file into a directory Add a second "allow_empty" mode to get_committed_file, which returns the empty string is the named file is actually a directory. This is used by the check_ident() function, which is ok since a directory can't contain any expanded idents, so there is nothing to check. Note that get_staged_file() ought to support this mode as well. Currently, running get_staged_file() on a directory actually returns the contents of the first file in the directory, which is a bug.