Banjo example in docs renders without stems on 2.16.2-1 OSX

[Bayard Randel]

> I'm not top posting.

% Stems should render based on example in docs, but do not on 2.16.2-1 in OSX.
% http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Banjo#Banjo

\new TabStaff <<
  \set TabStaff.tablatureFormat = #fret-number-tablature-format-banjo
  \set TabStaff.stringTunings = #banjo-open-g-tuning
  {
    \stemDown
    g8 d' g'\5 a b g e d' |
    g4 d''8\5 b' a'\2 g'\5 e'\2 d' |
    g4
  }
>>