Implement "freezeif"
Implement "freezeif"

	* src/parser/ugrammar.y: Implement "freezeif". This uses an
	explicit "at_" when desugaring, because embedded desugaring
	doesn't seem to work at this time.

aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi