[CM] Snd 19.0

[bil at ccrma.Stanford.EDU]

Snd 19.0

s7: added (*s7* 'history-enabled) at Kjetil's suggestion.
     deprecated s7_gc_unprotect (use s7_gc_unprotect_at).
     added weak-hash-table

The main visible s7 change:

hash-table* is now hash-table, and the old hash-table is gone.
This code can provide backwards compatibility except for some
corner cases involving map and for-each:

(when (string>=? (s7-version) "8.0")
   (define hash-table* hash-table)
   (define (hash-table . args)
     (apply hash-table* (map (lambda (x)
			      (values (car x) (cdr x)))
			    args))))


checked: sbcl 1.4.14|15

Thanks!: Kjetil Matheussen, James Hearon