'verify' iff it's used by a test module...

and replaces them with a new API verify(). As a result the regression
suite will also perform its tests in optimization mode.

Written by Marc-Andre Lemburg. Copyright assigned to Guido van Rossum.

<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.