bug#981: 23.0.60; doc of debug-on-error

["Drew Adams" <drew.adams@oracle.com>]

`debug-on-error' does not control what happens during Lisp rexpression
evaluation. But you cannot know this by looking at only the doc of
`debug-on-error'.  For example, evaluate this using either `C-x C-e'
in buffer *scratch or via `M-:':
(unwind-protect jjjjjjj (message "XXXX"))
 
`eval-expression-debug-on-error' is what controls this behavior. In
the Elisp manual, the doc for `debug-on-error' is on the same page as
the doc for `eval-expression-debug-on-error', but even so, a reader
might read only the `debug-on-error' part if that's what s?he is
looking up.
 
The `debug-on-error' description in the manual needs a "see below"
mention of `eval-expression-debug-on-error' and of the fact that
`debug-on-error' alone does not control what happens during such sexp
evaluation.
 
The `debug-on-error' doc string, likewise, needs to mention this and
cross-reference the doc string for `eval-expression-debug-on-error'.
 
I think what happened was that when `eval-expression-debug-on-error'
was introduced in Emacs 21 this doc dependency was overlooked - the
doc for `eval-expression-debug-on-error' was added but the doc for
`debug-on-error' was not updated accordingly. In Emacs 20,
`debug-on-error' is all there is, so its doc is complete and
sufficient.
 

In GNU Emacs 23.0.60.1 (i386-mingw-nt5.1.2600)
 of 2008-09-03 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --no-opt --cflags -Ic:/g/include
-fno-crossjumping'