#17: THM not registering some appearances of target string - FIX for
bug.
 * fixed above bug - see issue for bug explanation. 
 * added test assertions that led to this bug being found (so also #6)
 * made rng private (not sure why it wasn't in the first place...)
 * made sure each taihen/hentai test loop started with a fresh thm
this fix also fixes issue #8, making the issue obsolete; after this
bugfix, the stats-main shows convergence to 256 as expected.