Uses horizontal skylines in accidental placement (issue 6489086)

[k-ohara5a5a]

I like it, but we need to figure out what went wrong with
'accidental-tie.ly'.  There was some trickery involving holding space
open for the accidental that might be needed on the second note of a
tied pair, iff the tie is broken across lines.

Ted Ross' textbook puts the upper flat about 0.5 staff-space right of
the lower flat in fourths and fifths.


http://codereview.appspot.com/6489086/diff/1/lily/accidental-placement.cc
File lily/accidental-placement.cc (right):

http://codereview.appspot.com/6489086/diff/1/lily/accidental-placement.cc#newcode125
lily/accidental-placement.cc:125: // right is up because we're
horizontal
Okay, so why do we care about 'up'?  Oh, the "right"-most edge of the
horizontal-skyline is the top of the accidental glyph, which location we
use for priority.

http://codereview.appspot.com/6489086/