[COMMIT] Update some documentation, comments; add some entries to etc/NEWS

[Stephen J. Turnbull]

Aidan Kehoe writes:

 > etc/ChangeLog addition:
 > 
 > 2006-11-11  Aidan Kehoe  <kehoea at parhasard.net>
 > 
 > 	* NEWS:
 > 	Add information on set-charset-registries, and the change to
 > 	define-specifier-tag. 

Aidan, the entries you added to NEWS are very pretty, but they're way
too verbose considering the amount of stuff that needs to go in
eventually.  I don't care what Ilya thinks about this; if he's going
to be following CVS HEAD, he should be reading xemacs-beta and
xemacs-patches.  (N.B. The historical practice was that NEWS had a
czar, namely Hrvoje Nik?i?, and it all got written The Night Before
Christmas.)

A whole new API might deserve that much space, but these changes
should be summarized almost out of existence; just enough for Lisp
programmers to know to look at the docstrings or manual.  Oh, and you
*do* have the right to brag to the users (but keep it brief :-).  Eg,

** Performance enhancements

- Charset registries for XLFDs are now restricted to vectors of fixed
  registries, speeding up font lookup on X devices.

** API changes - internal

- `set-charset-registry' is deprecated in favor of `set-charset-registries'.
- `define-specifier-tag' gets an optional CHARSET-PREDICATE argument.