Apply two changes, systematically:

(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!

Modules/svmodule.c

@@ -1070,7 +1070,7 @@ initsv()
 	m = Py_InitModule("sv", sv_methods);
 	d = PyModule_GetDict(m);
 
-	SvError = PyString_FromString("sv.error");
+	SvError = PyErr_NewException("sv.error", NULL, NULL);
 	if (SvError == NULL || PyDict_SetItemString(d, "error", SvError) != 0)
-		Py_FatalError("can't define sv.error");
+		return;
 }