swift234

Progress on: <rdar://problem/19382878> Introduce new x? pattern

This introduces a new pattern, spelled "x?" which is sugar for
matching ".Some(x)".  It also changes the parser slightly so that
_ (the discard expr) is parsed as a unary expr instead of as an
expr.  This allows it to have postfix ? after it, which is important
in pattern contexts to support "case _?:".



Swift SVN r25907