scanner: sort the use of SYMBOL.
scanner: sort the use of SYMBOL.

	* src/parser/utoken.l (RETURN_ASSIGN_OP): Remove, now useless.
	(RETURN_OP): Use only when its argument is understandable by the
	precompiled symbols machinery.

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