Snd 19.8

In Snd, Tito fixed many Snd bugs, involving left-sample and right-sample,
  off-by-1 cases for mark-sample and selection-samples, a bug in s7_load, etc.

checked: sbcl 1.5.7

Thanks!: Kjetil Matheussen, David O'Toole, Tito Latini
