Fix 915. Adjust `_setColumns` to deep clone properly and only once on recursive nodes.
Add test and update history.
Fix 915. Adjust `_setColumns` to deep clone properly and only once on recursive nodes.
Add test and update history.
Fix typos.
Remove unused vars from test. Use public method for test instead of protected.
Merge branch 'dev-3.x' of github.com:yui/yui3 into dt-915
Merge branch 'dt-915' of github.com:apipkin/yui3 into dt-915

Conflicts:
	src/datatable/HISTORY.md
	src/datatable/tests/unit/assets/datatable-core-tests.js
Comment out test unsafe for CI.
Merge branch 'dev-3.x' of https://github.com/yui/yui3 into dt-915