task_batcher.item_failed_hook: fix method signature.
Merge pull request #267 from matthewrmshin/task_batcher.item_failed_hook.signature

task_batcher.item_failed_hook: fix method signature.
Fixed a minor bug in recent batch submit code.

The bug was dormant because err was never True.
Merge pull request #268 from hjoliver/minor-bug-fix-in-batch-submit

Fixed a minor bug in recent batch submit code.
Hot fix: recent typo in batch_submit.py

Caused abort after job submission failure. The new batch submission code
now works correctly for job submission and event handler failure.
Updated change log for 5.0.1
Minor change to change log formatting.