bug#3375: 23.0.94; Document incompatible change to format of bookmarks

Emacs 23 apparently introduces an incompatible change to the format of
bookmarks. A bookmark that formerly would have had this form:
("Directories"
  ((front-context-string . "\n22.8 File Direc")
   (rear-context-string . ": > Directories\n")
   (position . 133657)
   (filename . "c:/Emacs-23-0-3/info/emacs")
   (info-node . "Directories")
   (handler . Info-bookmark-jump)))
 
Now can have this form:
("Directories"
  (front-context-string . "\n22.8 File Direc")
  (rear-context-string . ": > Directories\n")
  (position . 133657)
  (filename . "c:/Emacs-23-0-3/info/emacs")
  (info-node . "Directories")
  (handler . Info-bookmark-jump))
 
The is handled in the changed definition of
`bookmark-get-bookmark-record', which accommodates both forms.
However, if you try to do, say, `C-x r l' in Emacs 22 and you have
created a bookmark of the latter form (using Emacs 23), then `C-x r l'
raises an error.  That's normal - Emacs 22 can't know about the
incompatible change that Emacs 23 introduces.
 
I don't know why this change was necessary. (Why?) But let's assume
that it was in fact necessary. The bug is that it is totally
undocumented.
 
Please _at least_ document this in NEWS. The _only_ thing mentioned in
NEWS about bookmarks is this:
 
 "*** bookmark provides `bookmark-make-record-function' so
 special major modes like Info can teach bookmark.el how to save
 and restore the relevant data."
 
 
 
In GNU Emacs 23.0.94.1 (i386-mingw-nt5.1.2600) of 2009-05-24 on
 SOFT-MJASON Windowing system distributor `Microsoft Corp.', version
 5.1.2600 configured using `configure --with-gcc (3.4)'