BUG: Do not manage our own list of subclasses.
Docstring.
Merge pull request #45 from enthought/fix-subclass-traits

BUG: Do not manage our own list of subclasses.
Fix a tuple leak in ctraits property constructor.

PyTuple_New() returns a new reference, which was incorrectly
being INCREFed in _trait_property in ctraits.c
Add a test case for the tuple leak in ctraits property.

Courtesy Robert Kern.