Allow occur command to operate on the region

See discussion in:
https://lists.gnu.org/archive/html/emacs-devel/2016-12/msg01084.html
* lisp/replace.el (occur--region-start, occur--region-end)
(occur--matches-threshold): New variables.
(occur-engine): Use them.
(occur): Idem.
Add optional arg REGION; if non-nil occur applies in that region.
* doc/lispintro/emacs-lisp-intro.texi (Keybindings): Update manual
* doc/emacs/search.texi (Other Repeating Search): Idem.
; etc/NEWS: Add entry for the new feature.

1 files changed, 3 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 86a8385ae76..dcefb75fd55 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -311,6 +311,9 @@ substituted by a home directory by writing it as "/foo:/:/~/file".
 * Editing Changes in Emacs 26.1
 
 +++
+** The 'occur' command can now operate on the region.
+
++++
 ** New bindings for 'query-replace-map'.
 'undo', undo the last replacement; bound to 'u'.
 'undo-all', undo all replacements; bound to 'U'.