* Add ContentCache test
* Use SemaphoreSlim as write lock
* Apply lock imrpovements to SnapDictionary
* Obsolete unused MonitorLock
(cherry picked from commit c3db3457e7)
* Add ContentCache test
* Use SemaphoreSlim as write lock
* Apply lock imrpovements to SnapDictionary
* Obsolete unused MonitorLock
(cherry picked from commit c3db3457e7)