Give \key command a better predicate for scale type
{ \key c major }
should not be accepted at the parsing state, turning "major" into
'(major) matching the list? predicate. So instead a number-pair-list?
predicate is being used which is much less likely to be matched by
erroneous input.
Diff:
Passes make, make check and a full make doc.
Patch on countdown for Nov 21
Patch counted down - please push.