Test for deletion actually ... deleting ... things.

Test for deletion actually ... deleting ... things.

Since we're using the DBI backend, everything's stored in the 'entries'
table in the SQLite database - which has, among other things, a 'class'
column storing the perl class of the entry. So I can run -

  SELECT class, COUNT(*) FROM entries GROUP BY class

to get the current counts in the database. I've altered the test to
collect these after the first tradition creation, after the second, and
after the deletion of the first - then added a loop to the end to check
that the final count is the second count minus the first for each class.

This seems to accurately reflect what we expect the database to look like
after a (successful) garbage collection run.