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.
Merge pull request #43 from pankajp/ctraits-property-tuple-leak

Fix a tuple leak in ctraits property constructor.