Devel cover

Enables -cover option with test-tracker.
I'd still like to refactor so that it works with either Redirect or Interactive (I have it set to work with Interactive only right now, but Redirect is also useful because some of the tests are still failing when run with Devel::Cover and it is helpful to see their output as I work to eliminate/work around the failures.
I added two new environment variables: TT_COVER_OUTPUT_DIR and TT_COVER_IGNORE_LIST (Is there a better way to pass in configuration options?)