[Go] Renamed/refactored Swigcptr<classname> (uintptr) to SwigClass<classname> (struct).

* First part of issue #289 to let Go track object ownership. This part renamed/refactored Swigcptr<classname> (uintptr) to SwigClass<classname> (struct) so that later an ownership boolean can be added to the struct.
* This change required two tests to be fixed because of hard-coded names.
* This change required one test to be disabled because a tiny bit more static type-checking is in place.