Log Message:
py-xcbgen, xcb-proto: update to 1.15.1

Also add comment that one should update both together.

Changes:

Austin Shafer (1):
      dri3: Update dri3.xml to DRI3 1.3

Matt Turner (1):
      xcb-proto 1.15.1

Mike Sharov (1):
      Add DOUBLE-BUFFER extension specification.