Another cyclic dependency in rest-collision.cc

[Neil Puttock]

Hi Joe,

Here's another one:

130       for (vsize i = 0; i < rests.size (); i++)
131         {
132           Grob *r = Note_column::get_rest (rests[i]);
133
134           Direction d = get_grob_direction (r);
135           if (d)
136             ordered_rests[d].push_back (rests[i]);

162       Real diff
163         = (ordered_rests[DOWN].back ()->extent (common, Y_AXIS)[UP]
164            - ordered_rests[UP].back ()->extent (common,
Y_AXIS)[DOWN]) / staff_space;

Line 164 triggers the same cyclic dependency for NoteColumn Y-extent.
This doesn't appear as straightforward as the last one, since changing
line 136 so it stores the rest instead of the note column breaks two
regression tests.

Cheers,
Neil