Revert revisions:

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.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index e2907e0..c29a61c 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -12,24 +12,6 @@
 #endif
 #include <signal.h>
 
-/* The POSIX spec requires that use of pthread_attr_setstacksize
-   be conditional on _POSIX_THREAD_ATTR_STACKSIZE being defined. */
-#ifdef _POSIX_THREAD_ATTR_STACKSIZE
-#ifndef THREAD_STACK_SIZE
-#define	THREAD_STACK_SIZE	0	/* use default stack size */
-#endif
-/* for safety, ensure a viable minimum stacksize */
-#define	THREAD_STACK_MIN	0x8000	/* 32kB */
-#if THREAD_STACK_MIN < PTHREAD_STACK_MIN
-#undef THREAD_STACK_MIN
-#define	THREAD_STACK_MIN	PTHREAD_STACK_MIN
-#endif
-#else  /* !_POSIX_THREAD_ATTR_STACKSIZE */
-#ifdef THREAD_STACK_SIZE
-#error "THREAD_STACK_SIZE defined but _POSIX_THREAD_ATTR_STACKSIZE undefined"
-#endif
-#endif
-
 /* The POSIX spec says that implementations supporting the sem_*
    family of functions must indicate this by defining
    _POSIX_SEMAPHORES. */   
@@ -156,10 +138,6 @@
 #if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
 	pthread_attr_t attrs;
 #endif
-#if defined(THREAD_STACK_SIZE)
-	size_t	tss;
-#endif
-
 	dprintf(("PyThread_start_new_thread called\n"));
 	if (!initialized)
 		PyThread_init_thread();
@@ -167,15 +145,8 @@
 #if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
 	pthread_attr_init(&attrs);
 #endif
-#if defined(THREAD_STACK_SIZE)
-	tss = (_pythread_stacksize != 0) ? _pythread_stacksize
-					 : THREAD_STACK_SIZE;
-	if (tss != 0) {
-		if (pthread_attr_setstacksize(&attrs, tss) != 0) {
-			pthread_attr_destroy(&attrs);
-			return -1;
-		}
-	}
+#ifdef THREAD_STACK_SIZE
+	pthread_attr_setstacksize(&attrs, THREAD_STACK_SIZE);
 #endif
 #if defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
         pthread_attr_setscope(&attrs, PTHREAD_SCOPE_SYSTEM);
@@ -489,33 +460,3 @@
 }
 
 #endif /* USE_SEMAPHORES */
-
-/* set the thread stack size.
- * Return 1 if an exception is pending, 0 otherwise.
- */
-static int
-_pythread_pthread_set_stacksize(size_t size)
-{
-	/* set to default */
-	if (size == 0) {
-		_pythread_stacksize = 0;
-		return 0;
-	}
-
-	/* valid range? */
-	if (size >= THREAD_STACK_MIN) {
-		_pythread_stacksize = size;
-		return 0;
-	}
-	else {
-		char warning[128];
-		snprintf(warning,
-			 128,
-			 "thread stack size of %#x bytes not supported",
-			 size);
-		return PyErr_Warn(PyExc_RuntimeWarning, warning);
-	}
-}
-
-#undef THREAD_SET_STACKSIZE
-#define THREAD_SET_STACKSIZE(x)	_pythread_pthread_set_stacksize(x)