0.pre8.85

0.pre8.85
	Merge the definitely-maybe-gc branch:

	Remove all the lispland logic that checks bytes-consed
	thresholds to see if it's worth GCing: C does these checks
	anyway.  SUB-GC now always GCs unless *GC-INHIBIT* says not to

	Delete the notify before/after calls and notify-stream.
	(Planned future change: pass the same information to
	*{BEFORE,AFTER}-GC-HOOKS* instead)

	*SOFT-HEAP-LIMIT* and MAYBE-GC are gone (unused).
	*ALREADY-MAYBE-GCING* is also dead, replaced with a proper
	mutex that will also prevent simultaneous GCs from multiple
	threads.  This entails moving gc.lisp and purify.lisp after
	target-thread in the build-order

	(Unithread WITH-MUTEX now honours its WAIT-P argument, so
	actually works in this situation)