Make querying to kill processes customizable

Introduce a new customization option, `confirm-kill-processes', that
users can set to nil if they don't want Emacs to nag them about killing
processes.

* lisp/files.el (confirm-kill-processes): New customization option.
(save-buffers-kill-emacs): Use customization option.

* test/lisp/files-tests.el
(files-test--save-buffers-kill-emacs--confirm-kill-processes): Add
test for new customization option.

* doc/emacs/entering.texi (Exiting): Document new user option.

* doc/lispref/processes.texi (Query Before Exit): Document new
user option.

* etc/NEWS: Document new user option.

1 files changed, 7 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index bc36d8ad3b9..bd94c943311 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -82,6 +82,13 @@ of a parenthetical grouping or string-delimiter: the default value nil
 keeps point at the end of the region, setting it to non-nil moves
 point to the beginning of the region.
 
++++
+** The new user option 'confirm-kill-processes' allows the user to
+skip a confirmation prompt for killing subprocesses when exiting
+Emacs.  When set to t (the default), Emacs will prompt for
+confirmation before killing subprocesses on exit, which is the same
+behavior as before.
+
 ---
 ** 'find-library-name' will now fall back on looking at 'load-history'
 to try to locate libraries that have been loaded with an explicit path