Script optimization maintenance and updates:

maintenance fixes for variadic run-time checks, '_' placeholder identifier
  "-O allow-cond" permits compiling scripts to C++ when influenced by @if conditionals
  more robust standalone compile-to-C++ properties
  fix for nested "when" statements
  test suite updates

src/Frame.h

@@ -194,6 +194,7 @@ public:
 		call = arg_call;
 		SetTriggerAssoc((void*)call);
 		}
+	void SetOnlyCall(const CallExpr* arg_call) { call = arg_call; }
 	const CallExpr* GetCall() const { return call; }
 
 	void SetTriggerAssoc(const void* arg_assoc) { assoc = arg_assoc; }