Thank you for review and for found bugs. I again checked the patch, corrected 
the errors and dubious places. Also I corrected the error in 
Modules/grpmodule.c (in other places gid_t parsed as signed long) and the 
possible behaviour change in Modules/_io/_iomodule.c, reversed the changes in 
Modules/pyexpat.c. If some changes cause you have doubts, you can cherry-pick 
only the most obvious fixes.

> Ideally, each fix there should be backed by a regression test.

Unfortunately I have only platforms where sizeof(int) == sizeof(long) == 
sizeof(size_t).