Added @Description to settings
Better error messages on configuration issues
Deprecated online_backup_port and replaced with online_backup_server which is a HostnamePort
More resurrected HA tests that were temporarily removed for HA 1.5.
Fixes issues that these new tests discovered:
o The cached contents in the IndexStore instance could become stale after
  copying a new store from the master. Solved by invalidating.
o Index locks (IndexLock) were silently ignored in the HA scenario,
  which made Index#putIfAbsent not atomic.