Implementation of the User32.PrintWindow

[Josselin Bardet]

Hi,

As next of the discussion on the bug 18772 
(http://bugs.winehq.org/show_bug.cgi?id=18772), I send here the 
implemenation for User32.PrintWindow function

I've tested it with an application that was crashing because of this 
unimplemented function.

Regards
Jos