Fixed an error in the suicide tutorial suite.
Warn on suiciding an active task.
Log suicides.
Don't retry task message send if task proxy not found in suite.
Merge pull request #837 from hjoliver/suicide-tutorial-typo

Fixed an error in the suicide tutorial suite.
Merge pull request #839 from hjoliver/834.suicide-warning

Log suicides, and warn if task is active at the time
Merge pull request #840 from hjoliver/836-unnecessary-messaging-retries

Don't retry task message send if task proxy not found in suite.
Merge branch 'master' into cylc.task-message-send-succeeded-bugfix