New pretest 21.0.90

[Gerd Moellmann]

The first pretest of Emacs 21 is available.  You can get it from

  <ftp://alpha.gnu.org/gnu/emacs/emacs-21.0.90.xtar.gz>
  <ftp://alpha.gnu.org/gnu/emacs/leim-21.0.90.xtar.gz>

(The directory containing the files isn't listable.)

There have been lots of changes since version 20, so basically
everything should be tested.  Please see etc/NEWS for a list of new
features, packages that were added etc.

If you're a C programmer, I'd like to draw your attention to the new
mechanism of conservative stack marking, which is currently known to
work for some systems---e.g. it's already the default for FreeBSD and
NetBSD---but it has not yet been ported to all systems.  I'd like to
have this working on as many systems as possible because it removes a
source of bugs that are especially hard to debug.  If you can help me
with this, please let me know.  The file alloc.c has a comment around
line 3350, in front of the function mark_stack, which hopefully
explains clear enough what has to be done to make conservative stack
marking work.

If you encounter performance problems, and absolutely can't live with
it, you can apply the following patch, which disables some debug code.
If you can, please let the debug code activated; it can help us track
down an obscure problem.

*** alloc.c     2000/10/27 12:01:21     1.228
--- alloc.c     2000/11/17 19:27:16
***************
*** 30,36 ****
     strings is redundantly recorded in sdata structures so that it can
     be compared to the sizes recorded in Lisp strings.  */
  
! #define GC_CHECK_STRING_BYTES 1
  
  /* GC_MALLOC_CHECK defined means perform validity checks of malloc'd
     memory.  Can do this only if using gmalloc.c.  */
--- 30,36 ----
     strings is redundantly recorded in sdata structures so that it can
     be compared to the sizes recorded in Lisp strings.  */
  
! /* #define GC_CHECK_STRING_BYTES 1 */
  
  /* GC_MALLOC_CHECK defined means perform validity checks of malloc'd
     memory.  Can do this only if using gmalloc.c.  */