- pack all button data in 2 bytes instead of 48
       - adjust the way we extract button data
       - query extended capabilities if SYN_EXT_CAP_REQUESTS >= 1
         (was == 1) according to Synaptics' addendum to the interfacing
         guide
       - do not announce or report BTN_BACK/BTN_FORWARD unless touchpad
         has SYN_CAP_FOUR_BUTTON in its capability flags