handlers "return void", according to ANSI C.
Removed the new Py_RETURN_FROM_SIGNAL_HANDLER macro.
Left RETSIGTYPE in the config stuff, because it's not clear to
me that others aren't relying on it (e.g., extension modules).
(1) Use PyErr_NewException("module.class", NULL, NULL) to create the
exception object.
(2) Remove all calls to Py_FatalError(); instead, return or
ignore the errors -- the import code now checks PyErr_Occurred()
after calling a module's init function, so it's no longer a
fatal error for the initialization to fail.
Also did some small cleanups, e.g. removed unnecessary test for
"already initialized" from initfpectl(), and unified
initposix()/initnt().
I haven't checked this very thoroughly, so while the changes are
pretty trivial -- beware of untested code!