Add DijitRegistry#getParent for compatibility with dijit._KeyNavContainer
CHANGES.md: note DijitRegistry#getParent
Fix #533: simplify selector event registration
selector: Add test to demonstrate #533
selector: guard against undefined element when switching column structure
CHANGES.md: note selector event hookup fix
Fix #520: Only display single page number when there is 1 page of results

Also suppress pagingTextBox in this case, since there's only one valid page
CHANGES.md: note Pagination single-page fix
ColumnSet: Expose necessary functions for putScroller and positionScroller