Correctly positions dots on rests that share a column with a beamed grob. (issue 5992073)

[k-ohara5a5a]

I got about halfway through, but then it got too complicated with the
various ways to compute the Dots' Y-offset under various conditions.


http://codereview.appspot.com/5992073/diff/5001/lily/dot-column.cc
File lily/dot-column.cc (right):

http://codereview.appspot.com/5992073/diff/5001/lily/dot-column.cc#newcode163
lily/dot-column.cc:163: are due to the fact that this callback is called
before line breaking
"this callback *may be* called"
There seems to be nothing enforcing that dot-positioning is done at any
particular time.

http://codereview.appspot.com/5992073/diff/5001/lily/dot-column.cc#newcode195
lily/dot-column.cc:195: int p = before_line_breaking &
Dots::in_dot_column_with_beam_and_rest (dp.dot_)
This looks suspicious at first. But it seems that whenever this specific
condition is true, get_rounded_position() would return 0 anyway.

http://codereview.appspot.com/5992073/diff/5001/lily/dot-column.cc#newcode203
lily/dot-column.cc:203:
It seems we want to just skip the collision resolution for dots on
rests, and let them ride with the rest, one position higher than the
center of the rest.
      if (Rest::has_interface (note))
        {
          cfg[p+1] = dp;
          continue;
        }

http://codereview.appspot.com/5992073/