This should prevent some test_multiprocessing failures

Heavily revised, comprising revisions:
46640 - original trunk revision (backed out in r46655)
46647 - markup fix (backed out in r46655)
46692:46918 merged from branch aimacintyre-sf1454481

branch tested on buildbots (Windows buildbots had problems
not related to these changes).

46640 Patch #1454481:  Make thread stack size runtime tunable.
46647 Markup fix

The first is causing many buildbots to fail test runs, and there
are multiple causes with seemingly no immediate prospects for
repairing them.  See python-dev discussion.

Note that a branch can (and should) be created for resolving these
problems, like

svn copy svn+ssh://svn.python.org/python/trunk -r46640 svn+ssh://svn.python.org/python/branches/NEW_BRANCH

followed by merging rev 46647 to the new branch.

Thanks to Skip Montanaro and Kalle Svensson for the patches.

This closes SF patch #504215.

This changes Pythread_start_thread() to return the thread ID, or -1
for an error.  (It's technically an incompatible API change, but I
doubt anyone calls it.)

This should match the situation in the 1.6b1 tree.

names in the source code (they already had those for the linker,
through some smart macros; but the source still had the old, un-Py names).

All per-thread globals are moved into a struct which is manipulated
separately.

use the new names exclusively, and the linker will see the new names.
Files that import "Python.h" also only see the new names.  Files that
import "allobjects.h" will continue to be able to use the old names,
due to the inclusion (in allobjects.h) of "rename2.h".

thread.h: use PROTO instead of _P for prototypes.

necessary, and when they are, use SIGKILL; when compiled with -DDEBUG,
only print debug messages when "THREADDEBUG" is set in the environment.

to avoid hanging in cleanup().

* split pythonmain.c in two: most stuff goes to pythonrun.c, in the library.
* new optional built-in threadmodule.c, build upon Sjoerd's thread.{c,h}.
* new module from Sjoerd: mmmodule.c (dynamically loaded).
* new module from Sjoerd: sv (svgen.py, svmodule.c.proto).
* new files thread.{c,h} (from Sjoerd).
* new xxmodule.c (example only).
* myselect.h: bzero -> memset
* select.c: bzero -> memset; removed global variable