pass return integer back out through exit

for testing of binaries later (and off course general correctness)
Some tests were using the fact that the interpreter was used, changed those to return ints rather than strings

test/support/risc_interpreter.rb

@@ -36,7 +36,7 @@ module Risc
 
     def get_return
       assert_equal Parfait::Message , @interpreter.get_register(:r0).class
-      @interpreter.get_register(:r0).return_value
+      @interpreter.get_register(:r1)
     end
 
     # do as many as given ticks in the main, ie main_at more
@@ -78,6 +78,11 @@ module Risc
       run_main("return #{input}")
     end
 
+    # get the return from the message (not exit code)
+    # exit code must be int
+    def get_message_return
+      @interpreter.get_register(:r8).return_value
+    end
     def run_main(input)
       @string_input = as_main(input)
       do_setup