[Ready] More mutations

Time to start expanding things.

This pass:
A needed upgrade to the debug-mutation code (it currently can't handle threshold-granting or post-threshold traits; this lets you grant/revoke thresholds manually)
The long-promised Ectothermic (like Cold-blooded, but now should grant bonus speed above 65F, needs Lizard)
Alpha gets a few more mundane traits to improve odds of getting Prime
Threshold safety-lock (no, it's not supposed to be a valid downgrade target)
Mutagen addiction, with Extra Bonus trait to make it nastier!
Post-threshold upgrade for Cattle: Ruminant->Grazer, letting you eat grass for minor (2 or 5) hunger boost
Restricts the Insanely stat-buffs to post-Threshold
Upgraded Masochist for the Medical category post-threshold
Pain-blocker for the Medical category post-threshold
Nastier venom for Arachnids (Yeah, I'll put in extra legs for 'em and for Insects once I work out what good they'd do)
Substance Tolerance, for those of us who don't mind less mileage per hit
Alcohol Metabolism, Subterranean boost (less Drunk, less Depressant, more Nutrition!)
Non-purifiable traits ought to resist not-in-category cancellation (75% chance to not be marked for deletion)
Enhanced statboosters for Prime folks
Cenobite lengthened out to a two-mutation run (total of three, counting Masochist); they now get noticeably lighter Pain debuffs (but they look horrid in the bargain, not that it matters much ATM)

Went through and apparently no actual merge conflicts with this.  Whenever you're ready, I guess.