Bad refs to rowColumnIndex and treeColumnIndex

[joneit]

These lines , the context forrowColumnIndex and treeColumnIndex should be this.grid.behavior (not this.grid).

This resulted in getColumnWidth() always returning the default column width instead of the actual column width (not obvious when the actual column with was the default).

This is a problem in develop, introduced in #598: fix keyboard navigation; it is not a problem in master.