Interpret #... inside of music lists as music instead of ignoring it

Interpret #... inside of music lists as music instead of ignoring it

One consequence is that you get a warning for things like

\revert Score.BarLine #'space-alist #'cue-clef

which actually reverts the whole of space-alist, then ignores #'cue-clef.

Another is that things like $(set-accidental-style "dodecaphonic")
can be written as #(set-accidental-style "dodecaphonic") without
getting ignored in most situations.

Void expressions (like most definitions, or the result of calling
\void) are still silently ignored since they are regarded as
intentional.