allow reverse syntax for >> (ie <<)

slot >> reg makes sense, being a slot_to_reg
but . . .
consistently use of << (as meaning assignment , =) also makes sense
allow both and let time tell which makes more sense

lib/mom/instruction/message_setup.rb

@@ -54,8 +54,7 @@ module Mom
     def get_message_to( builder )
       builder.build do
         space << Parfait.object_space
-        space[:first_message] >> next_message
-        #risc << Risc.slot_to_reg(source + "get next message" , space , :first_message , message)
+        next_message << space[:first_message]
       end
     end
     def nnop