Test GetGeometry rather than CreateWindow request

Rather than using the hack of waiting for 1 second for error with the
CreateWindow request, test the GetGeometry request instead. This also
test that replies are correctly received and unpacked.
Prefix method argument "buf"

Prefix the method argument "buf" to prevent name clashes in reply,
event, and error dispatchers.
Regenerate xproto

Regenerate xproto with the prefixed "buf" argument.
Do not generate empty classes

Skip generation of empty measurer, packer, unpacker, and dispatchers for
extensions without defined types, replies, events, or errors.