Re: Fixes note column skylines by adding a stem tremolo pure height function. (issue4754054)

[n . puttock]

http://codereview.appspot.com/4754054/diff/14001/lily/stem-tremolo.cc
File lily/stem-tremolo.cc (right):

http://codereview.appspot.com/4754054/diff/14001/lily/stem-tremolo.cc#newcode151
lily/stem-tremolo.cc:151: Stem_tremolo::pure_height (SCM smob, SCM, SCM)
SCM /* start */, SCM /* end */

I spoke too soon here.  This function isn't pure (despite the comment
noting that it's unsafe to get the true slope from the beam) since it
calls translated_stencil () which will look at the beam:

\relative c' {
  c8:16 c c c'
}

-> programming error: minimise_least_squares ():  Nothing to minimise
This means that vertical spacing is triggered
before line breaking

(and an unsloped beam)

untranslated_stencil () is probably OK here (it's already used for
ly:stem-tremolo::width).

http://codereview.appspot.com/4754054/