Merge pull request #398 from anna2130/master

Fixed _spec.js test
Add ensureBuffer helper for nodes.
Merge pull request #400 from hindessm/add-ensure-buffer-helper

Add ensureBuffer helper for nodes.
Merge master
Merge branch 'master' of https://github.com/node-red/node-red
Added required changes
Added default to operation property and changed primary argument to aggregation to msg.payload