Enable the tests and support of shared_ptr in them for C (which required
disabling a previously passing, because not doing anything, attributes
test which is currently broken for unrelated reasons).
For shared_ptr proxy proxy classes, add a protected method swigSetCMemOwn for modifying
the swigCMemOwn and swigCMemOwnDerived member variables which are used by various other
methods for controlling memory ownership.
Closes#230Closes#759
