The approach in Alexander's patch looks fine to me.  +1 on applying this patch if someone can test it on a platform where sizeof(long) > sizeof(Py_ssize_t), and also verify that there are current test failures that are fixed by this patch.  (If there are no such tests, we should add some.)

I've only tested this on machines with sizeof(long) == sizeof(Py_ssize_t) == 4 and sizeof(long) == sizeof(Py_ssize_t) == 8, which isn't really much of a test at all.

ked-tao, if you're still listening:  are you in a position to test Alexander's patch on a relevant machine?