1.0.45.5: life: fix slow compile.

1.0.45.5: life: fix slow compile.

* Committing a patch I once got from Nikodemus.  Without it my toy
takes more than a week to compile.  I've been using this since
November in production, seems to work well.  Should probably have made
it into 1.0.44.28.

;;; FASTP is a KLUDGE: SBCL used to update the current-conflict only
;;; for the read-only case, but switched at one point to always
;;; updating it. This generally speeds up the compiler nicely, but
;;; sometimes it causes an infinite loop in the updating machinery,
;;; We cheat by switching of the fast path if it seems we're looping
;;; longer then expected.