Intellij friendly error message
Docs and tests for Channel.end behaviour

* Worked out exactly how Channel.end is implemented
* Wrote tests to assert this behaviour
* Wrote docs to specify this behaviour
Adding support for play.editor like play1
Merge pull request #2387 from jroper/enumerator-channel-end

Docs and tests for Channel.end behaviour
Merge pull request #2176 from nraychaudhuri/intellij_friendly_error

Intellij friendly error message
Merge remote-tracking branch: upstream/master