Pull request by entrez: don't create a Pratchett novel by writing
"novel" or "paperback book" on a known blank spellbook with a magic
marker.
Blanking a novel produces a blank spellbook; there isn't any blank
novel. That's intentional. Writing "novel" on a blank spellbook
and getting a randomly chosen Pratchett one wasn't intentional.
Closes #761
resulting in an unintentional bias toward Str and away from Cha;
negligible effect on individual games but had a minor cumulative
effect across a large set of games
+using a marker to write "novel" or "paperback book" on a known blank spellbook
+ was producing a randomly chosen Pratchett novel; make it fail instead
Fixes to 3.7.0-x Problems that Were Exposed Via git Repository