hash cache keys to stay under memcached limit of 250 characters
remove references to 'broker'
include actual key in value to detect improbable hash collisions
Merge pull request #74 from metamx/fix-memcached-keys

Fix memcached key length
TaskQueue: Behavior tweaks, simplification

- Lock tasks on add if possible
- Detect "already added" using exception test instead of bookkeeping map
- Update task status after commitRunnable instead of before commitRunnable
Merge branch 'master' into task-stuff