Feathered beams do not work with knees

[Rune Zedeler]

When using a feathered kneed beam, the stems on the "upside down" part 
of the beam are too long, because they do not know that the beam is 
feathered and therefore extend all the way to the position that the beam 
would have had, had it not been feathered.

%%% begin %%%
\version "2.10.25"
\paper { ragged-right = ##t }
{
  \once \override Beam #'grow-direction = #LEFT
  c,32[ d, e, f, c''' d''' e''' f''']
}
%%% end %%%