FR: keystroke to cancel prefix sub-keymap

[Adam Spiers <orgmode@adamspiers.org>]

Suppose that I have a sub-keymap for custom agenda commands with
prefix 's', i.e. shortcuts 's1', 's2', 's3' and so on.  I might invoke
org-agenda, press 's', then change my mind and want to use another
custom command instead.  Currently, the only way of doing this would
be to press something like 'q' or C-g, then reinvoke org-agenda.  It
would be nice instead if there was a keystroke which simply returned
you to the first *Agenda Commands* buffer.  The following patch
demonstrates the required behaviour, but as you can see, is not a
particularly clean way of doing it.

http://www.adamspiers.org/cgi-bin/hg.cgi/org-pacific/rev/8fadf3f7ddda

# HG changeset patch
# User Adam Spiers <orgmode@adamspiers.org>
# Date 1198960339 0
# Node ID 8fadf3f7ddda7680bf0df572bdc48f7a0133ee14
# Parent 42a4c005ba9ce0df46b01b9571fff385a65ccae5
SPACE to cancel prefix sub-keymap

--- a/org.el	Sat Dec 29 20:32:19 2007 +0000
+++ b/org.el	Sat Dec 29 20:32:19 2007 +0000
@@ -19340,6 +19340,14 @@ L   Timeline for current buffer         
 	    (setq restriction nil))
 	   ((and (equal selstring "") (memq c '(?a ?t ?m ?L ?C ?e ?T ?M ?# ?! ?/)))
 	    (throw 'exit (cons (setq selstring (char-to-string c)) restriction)))
+           ((and (> (length selstring) 0) (eq c ? ))
+            (delete-window)
+            (org-agenda-get-restriction-and-command prefix-descriptions))
+;; Can't do it this way because help text describing hardcoded agenda
+;; commands is inserted into buffer outside the (while t ...) loop.
+;;             (setq selstring ""
+;;                   rmheader 0
+;;                   custom org-agenda-custom-commands))
 	   ((equal c ?q) (error "Abort"))
 	   (t (error "Invalid key %c" c))))))))