Make bug-reference-bug-regexp customizable

Ref: http://lists.gnu.org/archive/html/emacs-devel/2012-07/msg00427.html

* lisp/progmodes/bug-reference.el (bug-reference): New custom group.
(bug-reference-bug-regexp): Make it a defcustom.

lisp/ChangeLog

@@ -1,3 +1,8 @@
+2012-08-22  Glenn Morris  <rgm@gnu.org>
+
+	* progmodes/bug-reference.el (bug-reference): New custom group.
+	(bug-reference-bug-regexp): Make it a defcustom.
+
 2012-08-22  Daiki Ueno  <ueno@unixuser.org>
 
 	* progmodes/js.el (js-indent-level, js-expr-indent-offset)

lisp/progmodes/bug-reference.el

@@ -32,6 +32,11 @@
 
 ;;; Code:
 
+(defgroup bug-reference nil
+  "Hyperlinking references to bug reports"
+  ;; Somewhat arbitrary, by analogy with eg goto-address.
+  :group 'comm)
+
 (defvar bug-reference-map
   (let ((map (make-sparse-keymap)))
     (define-key map [mouse-2] 'bug-reference-push-button)
@@ -63,9 +68,13 @@ so that it is considered safe, see `enable-local-variables'.")
            (and (symbolp s)
                 (get s 'bug-reference-url-format)))))
 
-(defconst bug-reference-bug-regexp
+(defcustom bug-reference-bug-regexp
   "\\([Bb]ug ?#\\|[Pp]atch ?#\\|RFE ?#\\|PR [a-z-+]+/\\)\\([0-9]+\\(?:#[0-9]+\\)?\\)"
-  "Regular expression which matches bug references.")
+  "Regular expression matching bug references.
+The second subexpression should match the bug reference (usually a number)."
+  :type 'string
+  :safe 'stringp
+  :group 'bug-reference)
 
 (defun bug-reference-set-overlay-properties ()
   "Set properties of bug reference overlays."