More clock fixes.

[Olivier Fourdan]

Hi all,

I just committed a few more fixes to the clock widget. 

It is now possible to run several clock widgets w/out display updating
problems. It could be thread safe too, but not tested.

I've also moved the digits.xbm inside xfce_clock.c (like it was in
xfce3) because I want anybody to pick up xfce_clock.[ch] and get all
that is needed w/out requiring any additionnal files (like in including
the xbm from ../icons/)

Cheers,
-- 
Olivier               <fourdan at xfce.org>            http://www.xfce.org
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