memory leak in error handling

[robertwb]

Cached exceptions are not properly decreed when function returns from within try block.

%cython
def foo():
    try:
        return None
    except:
        pass

%python
def test():
    print get_memory_usage()
    for i in range(100000):
        try:
            foo()
            raise TypeError
        except TypeError:
            pass
    print get_memory_usage()

See also  http://trac.sagemath.org/sage_trac/ticket/4639

[robertwb]

See  http://hg.cython.org/cython/rev/66ce58e9ff83