Performance problem with large number of cell comments

1. Enter 1 in A1.
2. Add cell comment "Test" for A1.
3. Copy A1 into A2:A65536.

This takes a long time. Some fixes have been added, but it's still not a good as it should be. There is a O(n^2) problem.

Currently 80% is spent in scg_colrow_distance_get.