fix the exit sequence

was returning wrong register (1, not 0)
also saving the message for test, which changes order as the return value destroys the message

lib/risc/builtin/object.rb

@@ -78,10 +78,10 @@ module Risc
         # a sort of inline version of exit method.
         # Used by exit and __init__ (so it doesn't have to call it)
         def exit_sequence(builder)
-          r1 = RiscValue.new( :r1 , :Integer )
-          builder.add_slot_to_reg "get return" , :message , :return_value , r1
-          builder.reduce_int( "reduce return" , r1)
-          emit_syscall( builder  , :exit )
+          save_message( builder )
+          builder.add_slot_to_reg "get return" , :message , :return_value , :message
+          builder.reduce_int( "reduce return" , :message)
+          builder.add_code Syscall.new("emit_syscall(exit)", :exit )
         end
 
         def exit( context )