Forward-port of r52136: a review of overflow-detecting code. * unified the way intobject, longobject and mystrtoul handle values around -sys.maxint-1. * in general, trying to entierely avoid overflows in any computation involving signed ints or longs is extremely involved. Fixed a few simple cases where a compiler might be too clever (but that's all guesswork). * more overflow checks against bad data in marshal.c. * 2.5 specific: fixed a number of places that were still confusing int and Py_ssize_t. Some of them could potentially have caused "real-world" breakage. * list.pop(x): fixing overflow issues on x was messy. I just reverted to PyArg_ParseTuple("n"), which does the right thing. (An obscure test was trying to give a Decimal to list.pop()... doesn't make sense any more IMHO) * trying to write a few tests...