* lily/rests.ly: added comment on bogus warnings about missing flags
* lily/clef.cc, lily/rests.cc: added warning when font character
lookup fails.
* lily/rests.cc: workaround: consider missing ledgered rests in
ancient font.
* lily/rests.cc: bugfix: cleaned up font lookup code that handles
special cases of styles 'default' and 'classical'. This should
also fix the behaviour of lily/multi-measure-rest.cc, which so far
did not consider styles 'default' and 'classical'.