bug#24923: 25.1; Lisp watchpoints

[npostavs]

severity: wishlist
tags: patch

Continuing from
https://lists.nongnu.org/archive/html/emacs-devel/2015-11/msg01437.html,
main code difference since then is that I use a subr instead of indexing
into a table of C functions (the reason for using an index was to avoid
GC on Ffuncall; instead I did that by checking if the function is SUBRP
and doing funcall_subr on it (a new function extracted from Ffuncall)).

I've also added tests, which turned up some interesting corner cases
regarding aliases, and also that I had completely missed
kill-local-variables.

I still need to write something up in the manual.

v4-0001-Add-lisp-watchpoints.patch
Description: Text document

v4-0001-Add-lisp-watchpoints.patch
Description: Text document

v4-0002-Add-function-to-trigger-debugger-on-variable-writ.patch
Description: Text document

v4-0003-Ensure-redisplay-using-variable-watcher.patch
Description: Text document

v4-0004-Add-tests-for-watchpoints.patch
Description: Text document

v4-0005-etc-NEWS-Add-entry-for-watchpoints.patch
Description: Text document