change to_risc and builtin code according to last commit

Wherever space was loaded to get to the next_message
we now load the Message factory.
Otherwise much the same, only the attribute is next_object, not next_message
The binary is growing with 1k objects per factory, so i had to fix (hack) arm to handle bigger constants
close #14

test/support/risc_interpreter.rb

@@ -40,7 +40,7 @@ module Risc
     # how many instruction up until the main starts, ie
     # ticks(main_at) will be the label for main
     def main_at
-      19
+      20
     end
 
     def get_return