Fix #11512. Add an initial test suite for the cgitb, providing 75% coverage.

Patch by Robbie Clemons (robquad), produced at the PyCon 2011 sprints.
diff --git a/Misc/ACKS b/Misc/ACKS
index 3fb0d9d..378b60e 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -175,6 +175,7 @@
 Mike Clarkson
 Andrew Clegg
 Brad Clements
+Robbie Clemons
 Steve Clift
 Nick Coghlan
 Josh Cogliati