org-show-notification of org-clock.el broken on MS Windows

[Tim Schumacher <tim@datenknoten.me>]

Hi folks,

I have a snippet that clocks me in, if I set the TOOD-keyword of an item to
started. So some time after working on that item on and off, I got a stack trace
and it would not change the keyword to started. The error was, that emacs was
not compiled with dbus support and I thought, hell yeah, I'm on MS Windows, I
don't have dbus here. So I looked at the stack trace and found
org-clock-notify-once-if-expired which wants to show a notification if I took
longer than I estimated. Than digging deeper I found org-show-notification which
is where the actual error happens. It checks if the function
notifications-notify exists and then tries to use it. On my system the function
is available, but does not work because I don't have dbus support.

In my opinion these two actionable items should be done:

* The function org-show-notification should be more robust. It should not fail
  if it can't fire a notification for whatever reason.
* On MS Windows the function w32-notification-notify should be used.

Maybe someone has a quick fix, if not I can try my non existant elisp foo and hack
together a patch tomorrow, but please be gentle with me.

Thanks for your time and great effort into org-mode!

Tim