[CM] Snd 17.3

[bil at ccrma.Stanford.EDU]

Snd 17.3.

snd-init.el and snd-scheme-open-file from Orm Finnendahl.
More bug fixes from Tito.

s7: pair-line-number now returns #f if there is no line number.

checked: sbcl 1.3.15|16, gtk 3.89.5

Thanks!: Orm Finnendahl, Tito Latini, Daniel Hensel.