While it is still technically possible to test stage 0, it is not part of any
of the main testing rules and maintaining xfail-stage0 is a chore. Nobody
should worry about how tests fare in stage0.
ret is similar to fail: if not followed by an expression, it
should be parsed as a ret without an argument. The old version would
fail if ret was followed by a close paren (for example). Fixed it.
Closes#676.
