(PUP-1144) Make future parser accept $_private

This removes validation of QualifiedName (they must be validated
differently depending on where they appear). Variables were bit
by this too restrictive validation rule.
(PUP-1144) Fix up failing tests (pending new/better validation)

Two tests that expected validation to fail did not get triggered
because the too strict validation was removed. It needs to be replaced
with a different better validation. Such validation should be added
in 3.5 (too much work for 3.4) - instead, just accepting potentially
faulty names (they still have to lex correctly).