Fixes for property warnings generated in struct headers

Every struct generates warnings in the header because the properties are declared twice, once implicitly through the property declaration and once explicitly by the actual function declarations. This was done to increase compatibility with older versions of objective c that didn't have the ability to use the property syntax as it is declared now. This is harmless but you get two warnings per struct member, and in my case that worked out to a few hundred warnings.

The fix here is a simple refactor for isSet method declaration, and placing the declaration of the alternate getter/setter implementations into an #else statement beneath the currently existing #if statement, as opposed to just declaring them.