Switch to a lock for registry updates for better concurrency control
Log msg update
Refactored periodic registry update locking to:
- use a better name for the generational counter
- added additional fine grained locking around the getDelta code path
  to ensure more correct synchronisation
Adding log line for when client is configured to not register with the server
Make HealthCheckCallback injectable

Also change a few @Singleton's to @FineGrainedLazySingleton
Use Provider<HealthCheckCallback> to avoid circular dependencies
Fix NPE
Merge pull request #143 from qiangdavidliu/better-locking

Improved locking for periodic registry refreshes
Merge pull request #144 from elandau/master

Make HealthCheckCallback injectable
Fixes issue #145
Fixes issue #145
Merge pull request #146 from NiteshKant/master

Fixes issue #145
Fixes issue #147

Re-introducing read only response cache.
Merge pull request #148 from NiteshKant/master

Fixes issue #147
[Gradle Release Plugin] - pre tag commit:  '1.1.135'.
[Gradle Release Plugin] - new version commit:  '1.1.136-SNAPSHOT'.