Re: mensural notation improvements (issue3797046)

[benko . pal]

One thing I forgot to mention: I've also rewritten dot handling within
ligatures.  The old code
- didn't avoid staff lines
- didn't conform actual usage: dotting notes above is not a practice,
only if they are first within a flexa, see examples in
http://anaigeon.free.fr/mes_facs/fsbarb.jpg
http://upload.wikimedia.org/wikipedia/commons/d/d7/Eton_Choirbook.jpg

(actually I know one example when the second flexa note is dotted above,
but general usage is like the two above, when such notes are dotted
behind.)

http://codereview.appspot.com/3797046/