[Xcb] RFC: XInput2 extension support

[Daniel Martin]

Hi,

it took some time, but finally I'm able to present what I'm working on:

    XInput2 extension support for XCB.

Lots have requests and events have been tested and proven to work. But,
not all and not all of their details.
The naming scheme for field names is not that consistent as it should
be, but that's a minor and can (and will) be fixed soon.
More important are the protocol specialties xcbgen is unable to handle
in it's current state. Those issues have been described on top of the
protocol description and related fields have a "fixme_" prefix in the
name.

The patches are:
1. [RFC v0 proto] Add XInput2 protocol description
2. [PATCH libxcb] Add XInput2 extension support, disabled by default.

If you've some time you can spend, please review the protocol
description.


Thanks,
    Daniel Martin