Let `org-agenda-set-restriction-lock' remove restriction at point

* lisp/org-compat.el (org-speedbar-set-agenda-restriction):
* lisp/org-agenda.el (org-agenda-set-restriction-lock):
If there is an agenda restriction at point, remove it.

* doc/org-manual.org:
* etc/ORG-NEWS: Document the new feature.

doc/org-manual.org

@@ -8338,20 +8338,20 @@ scope for an extended period, use the following commands:
 
      #+kindex: C-c C-x <
      #+findex: org-agenda-set-restriction-lock
-     Permanently restrict the agenda to the current subtree.  When
-     called with a prefix argument, or with the cursor before the
-     first headline in a file, set the agenda scope to the entire
-     file.  This restriction remains in effect until removed with
-     {{{kbd(C-c C-x >)}}}, or by typing either {{{kbd(<)}}} or
-     {{{kbd(>)}}} in the agenda dispatcher.  If there is a window
-     displaying an agenda view, the new restriction takes effect
-     immediately.
+     Restrict the agenda to the current subtree.  If there already is
+     a restriction at point, remove it.  When called with a universal
+     prefix argument or with the cursor before the first headline in a
+     file, set the agenda scope to the entire file.  This restriction
+     remains in effect until removed with {{{kbd(C-c C-x >)}}}, or by typing
+     either {{{kbd(<)}}} or {{{kbd(>)}}} in the agenda dispatcher.  If there is a
+     window displaying an agenda view, the new restriction takes
+     effect immediately.
 
 - {{{kbd(C-c C-x >)}}} (~org-agenda-remove-restriction-lock~) ::
 
      #+kindex: C-c C-x >
      #+findex: org-agenda-remove-restriction-lock
-     Remove the permanent restriction created by {{{kbd(C-c C-x <)}}}.
+     Remove the restriction created by {{{kbd(C-c C-x <)}}}.
 
 #+texinfo: @noindent
 When working with =speedbar.el=, you can use the following commands in
@@ -8360,15 +8360,16 @@ the Speedbar frame:
 - {{{kbd(<)}}} (~org-speedbar-set-agenda-restriction~) ::
 
      #+findex: org-speedbar-set-agenda-restriction
-     Permanently restrict the agenda to the item---either an Org file
-     or a subtree in such a file---at the cursor in the Speedbar
-     frame.  If there is a window displaying an agenda view, the new
-     restriction takes effect immediately.
+     Restrict the agenda to the item---either an Org file or a subtree
+     in such a file---at the cursor in the Speedbar frame.  If agenda
+     is already restricted there, remove the restriction.  If there is
+     a window displaying an agenda view, the new restriction takes
+     effect immediately.
 
 - {{{kbd(>)}}} (~org-agenda-remove-restriction-lock~) ::
 
      #+findex: org-agenda-remove-restriction-lock
-     Lift the restriction.
+     Remove the restriction.
 
 ** The Agenda Dispatcher
 :PROPERTIES:

etc/ORG-NEWS

@@ -298,6 +298,13 @@ parameters.  See example bellow.
   ,#+END_SRC
 #+END_SRC
 
+*** ~org-agenda-set-restriction-lock~ toggle agenda restriction at point
+
+You can set an agenda restriction lock with =C-x C-x <= or with =<= at the
+beginning of a headline when using Org speed commands.  Now, if there
+is already a restriction at point, hitting =<= again (or =C-x C-x <=) will
+remove it.
+
 ** New functions
 
 *** ~org-insert-structure-template~

lisp/org-agenda.el

@@ -7124,11 +7124,18 @@ Argument ARG is the prefix argument."
 
 ;;;###autoload
 (defun org-agenda-set-restriction-lock (&optional type)
-  "Set restriction lock for agenda, to current subtree or file.
-Restriction will be the file if TYPE is `file', or if type is the
-universal prefix \\='(4), or if the cursor is before the first headline
-in the file.  Otherwise, restriction will be to the current subtree."
+  "Set restriction lock for agenda to current subtree or file.
+When in a restricted subtree, remove it.
+
+The restriction will span over the entire file if TYPE is `file',
+or if type is '(4), or if the cursor is before the first headline
+in the file. Otherwise, only apply the restriction to the current
+subtree."
   (interactive "P")
+  (if (and org-agenda-overriding-restriction
+	   (member org-agenda-restriction-lock-overlay
+		   (overlays-at (point))))
+      (org-agenda-remove-restriction-lock 'noupdate)
     (org-agenda-remove-restriction-lock 'noupdate)
     (and (equal type '(4)) (setq type 'file))
     (setq type (cond
@@ -7160,7 +7167,7 @@ in the file.  Otherwise, restriction will be to the current subtree."
       (move-marker org-agenda-restrict-begin nil)
       (move-marker org-agenda-restrict-end nil)
       (message "Locking agenda restriction to file"))
-  (setq current-prefix-arg nil)
+    (setq current-prefix-arg nil))
   (org-agenda-maybe-redo))
 
 (defun org-agenda-remove-restriction-lock (&optional noupdate)

lisp/org-compat.el

@@ -688,6 +688,8 @@ This also applied for speedbar access."
 
 (defun org-speedbar-set-agenda-restriction ()
   "Restrict future agenda commands to the location at point in speedbar.
+If there is already a restriction lock at the location, remove it.
+
 To get rid of the restriction, use `\\[org-agenda-remove-restriction-lock]'."
   (interactive)
   (require 'org-agenda)
@@ -698,7 +700,11 @@ To get rid of the restriction, use `\\[org-agenda-remove-restriction-lock]'."
       (setq m (get-text-property p 'org-imenu-marker))
       (with-current-buffer (marker-buffer m)
 	(goto-char m)
-	(org-agenda-set-restriction-lock 'subtree)))
+	(if (and org-agenda-overriding-restriction
+		 (member org-agenda-restriction-lock-overlay
+			 (overlays-at (point))))
+	    (org-agenda-remove-restriction-lock 'noupdate)
+	  (org-agenda-set-restriction-lock 'subtree))))
      ((setq p (text-property-any (point-at-bol) (point-at-eol)
 				 'speedbar-function 'speedbar-find-file))
       (setq tp (previous-single-property-change