Tweak lookahead and schedule ahead time.
Tweak lookahead and schedule ahead time.

 * Try to reduce the chance of lag in the tick processing. Probably
   still need to improve, but it plays with little or no lag warnings on
   my old Macbook, songs tested, onward.xm, claustrophobia.xm and
   virtual dream.xm.

pgregory/wetracker,pgregory/wetracker