Spacing with empty contexts; issue 1669 (issue4515158)

[joeneeman]

http://codereview.appspot.com/4515158/diff/2009/lily/align-interface.cc
File lily/align-interface.cc (right):

http://codereview.appspot.com/4515158/diff/2009/lily/align-interface.cc#newcode222
lily/align-interface.cc:222: dy = max (dy, min_distance);
If pure is true, there may be some staves that are going to be removed.
However, these staves won't be removed until after line-breaking. Now,
they're thrown away because they have an empty skyline but if you change
that, you'll probably need to add a check here, before including padding
and min_distance.

A good way to check that it's working would be to add annotate-spacing =
##t to input/regression/hara-kiri-staff.ly and check that the
Y-extent-estimates are accurate.

http://codereview.appspot.com/4515158/diff/2009/lily/align-interface.cc#newcode229
lily/align-interface.cc:229: // So if stretchability=0, treat
basic-distance as a minimum-distance.
This is no longer needed, right?

http://codereview.appspot.com/4515158/