XInput changes for GTK+-1.4

[Owen Taylor <otaylor redhat com>]

Being about to make some binary-incompatible changes to the GdkEvent
structures, I thought I'd work on figuring out the changes to 
XInput support (which will also involve GdkEvent structure changes)
for GTK+-1.4.

The primary motivation for such changes is supporting the extra valuators
from the Wacom Intuos tables, but there also is some definite
cleanup of the API's possible, and it may also be desirable to 
make some changes to make the API abstract better on top of both
XInput and the Win32 tablet support that Tor has added.

I've put a description of my ideas at:

 http://www.gtk.org/~otaylor/gtk/1.4/xinput.html

This tries to address the extra-valuator problem, but doesn't
go very far in addressing the problem of configuration. In
fact, we probably need some extensions to the XInput extension
to allow for properly dealing with the configuration problem,
since the driver knows things like the type of each valuator
(location, pressure, tilt, wheel position) and also the
type of the device, but there is no way of conveying that
information to client applications or toolkits.

Regards,
                                        Owen