Issue 3489: Let \cue... use quoted-context-type of CueVoice consistently

Issue 3489: Let \cue... use quoted-context-type of CueVoice consistently

Previously Voice was used and this relied on a a CueVoice purportedly
being created by cue-substitute itself and providing a Voice alias.
There is a regtest input/regression/quote-tuplet-end.ly which relied
on an explicit Voice = "cue" serving as a substite catch for the cue
notes, effectively turning \cueDuring into \quoteDuring.  This kind of
usage is rather bizarre, and since it diverts the \voiceOne/\voiceTwo
settings for the cue voice into a CueVoice context anyway (which is
otherwise empty), the cue voice is still missing proper directional
information.  This was not worth supporting.

Regularizing the usage in this manner will reliably stop \quoteDuring
from introducing surprise CueVoice contexts.

Issue 3489: Let \quoteDuring descend to bottom context for its output

Also regularizes interpretation of quoted-context-id.  This patch by
itself does not resolve the issue since a CueContext is created in
any case, serving as Bottom and Voice context.  A followup patch
fixes that.

[dak, 2013-08-21 07:29:12]

Fix music display method

[lemzwerg, 2013-08-21 07:33:18]

LGTM.