Stack-allocated objects again (+benchmark)

[Dmitry Antipov]

1) In r117971, I've made an attempt to follow KISS principle and
redesign this stuff for simplicity and speed rather than versatility.

2) I am constantly asked about benchmarks.  OK, running this code:

(defun put-property-benchmark ()
  (interactive)
  (setq buffer-undo-list t)
  (let ((oldgc gcs-done)
        (oldtime (float-time)))
    (while (re-search-forward "[a-f0-9]+" nil t)
      (put-text-property (match-beginning 0) (match-end 0)
                         'face 'font-lock-comment-face))
    (message "GCs: %d Elapsed time: %f seconds"
             (- gcs-done oldgc) (- (float-time) oldtime))))

through a ~35M dump generated with

od -v -t x2 < glibc-2.19.tar.xz > glibc.txt

shows 55GCs/23.7s with USE_STACK_LISP_OBJECTS and 66GCs/27.9s
without them.  Hopefully this simple benchmark is "real enough".

Dmitry