implement smaller than comparison

which is NOT an operator in the risc sense
rather a minus and a check for sign
(which _could be more efficient in arm, with conditional execution)

lib/risc/builder.rb

@@ -114,7 +114,7 @@ module Risc
       add_slot_to_reg(source , int_arg , at + 1, int_arg ) #1 for type
       return int_arg
     end
-
+    
     # assumed Integer in given register is replaced by the fixnum that it is holding
     def reduce_int( source , register )
       add_slot_to_reg( source + "int -> fix" , register , Parfait::Integer.integer_index , register)