Setup.in: added tkinter; rearranged the definition of PYTHONPATH so

Setup.in: added tkinter; rearranged the definition of PYTHONPATH so
that the module-specific components are in the section for that
module.

cursesmodule.c: patched it so it actually works.

tkintermodule.c: call Py_AtExit instead of atexit().

signalmodule.c: converted to new naming style; added
BGN/END SAVE around pause() call.

socketmodule.c: added setblocking() after Tommy Burnette.