Issue 5381: fix regression in pure python code path, Issue 5584: fix a decoder bug for unicode float literals outside of a container

as well as stringobject.c.

on systems with sizeof(int) > 4.

with fabs(x) >= 1e50, and fix documentation.

This adds a --randseed option, and makes regrtest.py -r indicate what random seed it's using so that that value can later be fed back to --randseed. This option is useful for tracking down test order-related issues found by make buildbottest, for example.

defined (part of issue #5035)

most significantly apply a modified portion of the patch from #4242 with
patches for skipping implementation details