Adding unit test for partial stepping into undefined context
Make compiled templates backward compatible with dust runtines prior to  2.2.0
Make compiled templates backward compatible with dust runtines prior to  2.2.0
Adding unit test for partial stepping into undefined context
Adding unit test for partial stepping into undefined context
Fix _get issue with empty context head;Generate 2.2.6 dist files
Fix _get issue with empty context head
Merge pull request #419 from kate2753/_getEmptyContextHead

Fix Context.prototype._get to work with context switching when calling partials and make the 2.2.x+ compiler fully backwards compatible.