org-clock.el: New option `org-clock-x11idle-program-name'

* org-clock.el (org-clock-x11idle-program-name): New option.
(org-x11idle-exists-p, org-x11-idle-seconds): Use it.

* org.texi (Resolving idle time): Document
`org-clock-x11idle-program-name'.

Debian and other OSes already have a program called 'xprintidle',
which does the same thing as x11idle. It also handles the DPMS bug[1]
some version of X servers have.

In order to use an alternative, introduce a customizable variable
'org-clock-x11idle-program-name' to hold the actual command name.

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502226

doc/org.texi

@@ -6322,6 +6322,7 @@ would be
 
 @subsubheading Resolving idle time
 @cindex resolve idle time
+@vindex org-clock-x11idle-program-name
 
 @cindex idle, resolve, dangling
 If you clock in on a work item, and then walk away from your
@@ -6335,12 +6336,14 @@ as 10 or 15, Emacs can alert you when you get back to your computer after
 being idle for that many minutes@footnote{On computers using Mac OS X,
 idleness is based on actual user idleness, not just Emacs' idle time.  For
 X11, you can install a utility program @file{x11idle.c}, available in the
-@code{contrib/scripts} directory of the Org git distribution, to get the same
-general treatment of idleness.  On other systems, idle time refers to Emacs
-idle time only.}, and ask what you want to do with the idle time.  There will
-be a question waiting for you when you get back, indicating how much idle
-time has passed (constantly updated with the current amount), as well as a
-set of choices to correct the discrepancy:
+@code{contrib/scripts} directory of the Org git distribution, or install the
+@file{xprintidle} package and set it to the variable
+@code{org-clock-x11idle-program-name} if you are running Debian, to get the
+same general treatment of idleness.  On other systems, idle time refers to
+Emacs idle time only.}, and ask what you want to do with the idle time.
+There will be a question waiting for you when you get back, indicating how
+much idle time has passed (constantly updated with the current amount), as
+well as a set of choices to correct the discrepancy:
 
 @table @kbd
 @item k

lisp/org-clock.el

@@ -396,6 +396,19 @@ specifications than `frame-title-format', which see."
   :group 'org-clock
   :type 'sexp)
 
+(defcustom org-clock-x11idle-program-name "x11idle"
+  "Name of the program which prints X11 idle time in milliseconds.
+
+You can find x11idle.c in the contrib/scripts directory of the
+Org git distribution. Or, you can do:
+
+    sudo apt-get install xprintidle
+
+if you are using Debian."
+  :group 'org-clock
+  :version "24.3"
+  :type 'string)
+
 (defvar org-clock-in-prepare-hook nil
   "Hook run when preparing the clock.
 This hook is run before anything happens to the task that
@@ -1034,13 +1047,13 @@ If `only-dangling-p' is non-nil, only ask to resolve dangling
 (defvar org-x11idle-exists-p
   ;; Check that x11idle exists
   (and (eq window-system 'x)
-       (eq (call-process-shell-command "command" nil nil nil "-v" "x11idle") 0)
+       (eq (call-process-shell-command "command" nil nil nil "-v" org-clock-x11idle-program-name) 0)
        ;; Check that x11idle can retrieve the idle time
-       (eq (call-process-shell-command "x11idle" nil nil nil) 0)))
+       (eq (call-process-shell-command org-clock-x11idle-program-name nil nil nil) 0)))
 
 (defun org-x11-idle-seconds ()
   "Return the current X11 idle time in seconds."
-  (/ (string-to-number (shell-command-to-string "x11idle")) 1000))
+  (/ (string-to-number (shell-command-to-string org-clock-x11idle-program-name)) 1000))
 
 (defun org-user-idle-seconds ()
   "Return the number of seconds the user has been idle for.