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/NEWS b/Misc/NEWS
index b96ca50..f742f8a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -994,6 +994,8 @@
 Tests
 -----
 
+- Issue #11512: Add a test suite for the cgitb module. Patch by Robbie Clemons.
+
 - Issue #12497: Install test/data to prevent failures of the various codecmaps
   tests.