XEmacs-friendly version of message-strip-forbidden-properties

[Hrvoje Niksic <hniksic@xemacs.org>]

Some time ago I noticed that inserting largeish chunks of text
(e.g. with C-x i) was quite slow in message buffers.  I traced the
slowness to after-change-functions set by message, namely
message-strip-forbidden-properties.  Leaving aside my personal
thoughts on whether this approach to removing forbidden properties is
necessary or even desirable, I noticed that the function iterates the
inserted region char by char and calls text property functions on each
character.  This cannot be fast when inserting regions containing
thousands of characters.

This is a version for XEmacs that explicitly iterates over extents in
the inserted region and therefore takes time proportional to the
number of extents therein (typically none, but in any case much
smaller than the number of characters).  With this inserting very
large files is again fast.  This function should probably be placed in
messagexmas, if you agree.

(defun message-strip-forbidden-properties (begin end &optional old-length)
  "Strip forbidden properties between BEGIN and END, ignoring the third arg.
This function is intended to be called from `after-change-functions'.
See also `message-forbidden-properties'."
  (when (and message-strip-special-text-properties
	     (message-tamago-not-in-use-p begin))
    (let ((plist message-forbidden-properties))
      (while plist
	(map-extents
	 (lambda (extent ignored)
	   (set-extent-property extent (car plist) nil)
	   nil)
	 nil begin end nil nil (car plist))
	(pop plist)
	(pop plist)))))