Collision between flags on down-stems and note-heads in single-staff polyphony

[Connor Harris]

\version "2.14.1"

%{ LilyPond can create collisions in single-staff polyphony when the
down-stemmed voice is higher than the up-stemmed voice and the down-stemmed
voice contains note-stems with flags. Here, for example, the B in voice one is
on top of the flag on the first F. I've included the similar problem from bug
no. 39 for comparison. %}

\relative c''{
  << {c4 b a2} \\ {g'4 f8\noBeam f e2}  >> \noBreak
  << c64 \\ c1 >>
}