Bug #128475: mimetools.encode (sometimes) fails when called from a thread.

pythonrun.c:  In Py_Finalize, don't reset the initialized flag until after
the exit funcs have run.
atexit.py:  in _run_exitfuncs, mutate the list of pending calls in a
threadsafe way.  This wasn't a contributor to bug 128475, it just burned
my eyeballs when looking at that bug.

Lib/atexit.py

@@ -16,9 +16,8 @@ def _run_exitfuncs():
     """
 
     while _exithandlers:
-        func, targs, kargs = _exithandlers[-1]
+        func, targs, kargs = _exithandlers.pop()
         apply(func, targs, kargs)
-        _exithandlers.remove(_exithandlers[-1])
 
 def register(func, *targs, **kargs):
     """register a function to be executed upon normal program termination

Python/pythonrun.c

@@ -181,9 +181,18 @@ Py_Finalize(void)
 
 	if (!initialized)
 		return;
-	initialized = 0;
 
+	/* The interpreter is still entirely intact at this point, and the
+	 * exit funcs may be relying on that.  In particular, if some thread
+	 * or exit func is still waiting to do an import, the import machinery
+	 * expects Py_IsInitialized() to return true.  So don't say the
+	 * interpreter is uninitialized until after the exit funcs have run.
+	 * Note that Threading.py uses an exit func to do a join on all the
+	 * threads created thru it, so this also protects pending imports in
+	 * the threads created via Threading.
+	 */
 	call_sys_exitfunc();
+	initialized = 0;
 
 	/* Get current thread state and interpreter pointer */
 	tstate = PyThreadState_Get();