Fixing wintab window messaging, bug 11846. Requesting review

[John Klehm]

Hey,

Well I'm trying to nail down why sai paint tool isn't doing its
pressure stuff and I think this is starting down the right track but I
wanted to get some input from those more familiar with wine messaging
and x11 events.

Without the first patch sai can't find an x11 window to attach too and
doesn't have any shot at all at getting pressure events from x11.

After that patch is applied it attaches to an x11 window but then
doesn't pass the information back to the child window that the wintab
context was created in.  The second patch implements an
EnumChildWindows callback function in order to get it back to the
child window.

I'm asking for this review as while the above works to get the
pressure events flowing I'm not sure if its the appropriate way to go.
 I believe these patches are on the path to fix
http://bugs.winehq.org/show_bug.cgi?id=11846

Thanks,

John Klehm