Added the atexit module and documentation from Skip Montanaro
<skip@mojam.com>.  Revisions to the markup to make it pass LaTeX, added
an index entry and a reference from the sys.exitfunc documentation.

This closes SourceForge patch #100620.
diff --git a/Lib/test/test_atexit.py b/Lib/test/test_atexit.py
new file mode 100644
index 0000000..517610b
--- /dev/null
+++ b/Lib/test/test_atexit.py
@@ -0,0 +1,24 @@
+# Test the exit module
+from test_support import verbose
+import atexit
+
+def handler1():
+    print "handler1"
+
+def handler2(*args, **kargs):
+    print "handler2", args, kargs
+
+# save any exit functions that may have been registered as part of the
+# test framework
+_exithandlers = atexit._exithandlers
+atexit._exithandlers = []
+
+atexit.register(handler1)
+atexit.register(handler2)
+atexit.register(handler2, 7, kw="abc")
+
+# simulate exit behavior by calling atexit._run_exitfuncs directly...
+atexit._run_exitfuncs()
+
+# restore exit handlers
+atexit._exithandlers = _exithandlers