RFC: Raw-Input Support

[Derek Lesho]

Hello, attached is a patch that adds true raw-input support for mouse
movements, bypassing the desktop's sensitivity and mouse acceleration
settings.

It is mostly complete, however I'd like some input on how I should get
retain compatibility with non winex11 display drivers.

My idea is to have all display drivers that support any kind of native raw
input send a raw input message to wineserver w/ a special flag set and w/
the structure specifying which raw-input events the display driver
supports.

For example in the case of x11/xinput2, we'd set hw_rawinput_t.mouse.x to 1
indicating that we intend to send native raw movement events.

What do you guys think about this approach?