Some minor fixes

Author: NlightNFotis

src/goto-symex/symex_assign.cpp

@@ -38,7 +38,7 @@ void goto_symext::symex_assign(
     if(statement==ID_function_call)
     {
       DATA_INVARIANT(
-      	!side_effect_expr.operands().empty()
+      	!side_effect_expr.operands().empty(),
       	"function call stamement expects non-empty list of side effects");
 
       if(side_effect_expr.op0().id()!=ID_symbol)

src/goto-symex/symex_start_thread.cpp

@@ -18,10 +18,9 @@ void goto_symext::symex_start_thread(statet &state)
   if(state.guard.is_false())
     return;
 
-  // we don't allow spawning threads out of atomic sections
-  // this would require amendments to ordering constraints
-  INVARIANT(state.atomic_section_id==0,
-    "start_thread in atomic section detected");
+  INVARIANT(state.atomic_section_id == 0,
+    "spawning threads out of atomic sections is not allowed; "
+    "this would require amendments to ordering constraints");
 
   // record this
   target.spawn(state.guard.as_expr(), state.source);