Keep track of button changes. Send the extended 4-byte messages for
three button mice only in case we have something to report for the
middle button. Use the short 3-byte messages (original protocol for
two-button microsoft mouse) otherwise.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1467625375-31774-5-git-send-email-kraxel@redhat.com