Attributes defined in extension modules via PyGetSetDef
aren't instances of property and aren't really handled
correctly in the above three modules.

This patch adds a types.GetSetterType an
inspect.isgetsetter() function, and support for
getsetters in pydoc, along with test cases and doc changes.

This patch should go into Python 2.5 and part of it
should get backported to Python 2.4.  Specifically the
support for PyGetSetDef in pydoc should be backported,
but it should be done in such a way as to not add
isgetsetter() or GetSetterType (fairly easy to do as
module globals in pydoc.py).

Mostly I'm looking for another set of eyes to proof my
changes.