Improve comments in symex-goto

Author: Owen

src/goto-symex/symex_goto.cpp

@@ -216,7 +216,7 @@ void goto_symext::symex_goto(statet &state)
     return;
   }
 
-  // put into state-queue
+  // put a copy of the current state into the state-queue
   framet::goto_state_listt &goto_state_list =
     state.top().goto_state_map[new_state_pc];