add a flag to skip the detective cases

[mapledyne]

To add a parallel to the yz_do_lovetunnel and yz_do_gingerbread to turn on/off the detective cases. Can't think of a good reason not to do them, but I didn't think that about the love tunnel either, forgetting about the password search. Adding this flag seems like a better "plays well" thing, and not too hard to do.
"yz_do_precinct" or some such.