Indented and repaired the maze of #ifdefs setting USE_RECURSION_LIMIT.

Indented and repaired the maze of #ifdefs setting USE_RECURSION_LIMIT.
Indented because it was incomprehensible.  "Repaired" means someone
checked in a change that screwed up the multiple nesting levels, causing
USE_RECURSION_LIMIT to stop getting defined on all non-LP64 boxes other
than FreeBSD.  Tried to repair that in a more-robust way.  That error
in turn caused a bogus change to get checked in to test_re.py, which I
repaired earlier.

This needs fresh testing on all non-Win32 platforms (Win32 never used
USE_RECURSION_LIMIT, and still doesn't).  Running the standard test_re.py
is an adequate test.