If the argument to make_file can act like a file, return it.
This is useful for code that calls command functions, but doesn't
want to send I/O through the filesystem.
include hg
recursive-include mercurial *.py
include hgweb.cgi
include hgeditor rewrite-log
include tests/README tests/run-tests tests/test-*[a-z] tests/*.out
include *.txt
include templates/map templates/map-*[a-z]
include templates/*.tmpl
include doc/README doc/*.txt
recursive-include contrib *
include README
include CONTRIBUTORS
include COPYING
include TODO
include MANIFEST.in