This tunable allows one to enable (1) or disable (0) gestures like tap
and tap-hold on Synaptics TouchPad when the Extended mode isn't enabled
(ie. "hw.psm.synaptics_support" not set).
By default, the value is -1 in order to keep the current behaviour of
not enabling/disabling gestures explicitly.
PR: kern/139272
Submitted by: David Horn <dhorn2000 AT gmail DOT com>
Reviewed by: David Horn <dhorn2000 AT gmail DOT com>
b469a43897