IndexerDBCoordinator: Work around SELECT -> INSERT races when adding segments
pom.xml: Update emitter
Indexing service: Break up segment actions

Each one now one operates on at most a collection of segments that comprise
a single partition. The main purpose of this change is to prevent audit log
payload sizes from getting out of control.
Empty task intervals, and empty lock intervals, aren't useful.

So prevent them from being created, through checks in AbstractFixedIntervalTask
and TaskLockbox.tryLock.
DbTaskStorage: Protect against invalid lock_payload
TaskActionToolbox: Combine adjacent ifs
Merge pull request #338 from metamx/indexing-service-bugs

Indexing service bugs