Fixed the an objective C test case so it passes correctly.

Fixed the test case to use a runtime function prototype that will be correct ([NSString stringWithCString: "new"]) instead of one that won't (expression str = [NSString stringWithFormat: @"%cew", 'N']). The runtime doesn't track vararg functions correctly so we can't reconstitute the function correctly.

Also fixed some expressions that used "str_id" whose type was "id" and do the necessary casting since "id" doesn't have any methods.