start impl issue 1947
not finished yet
issue 1947 (replication ) fix
RavenDB-1307 Added the low memory notification
RavenDB-1307 Clear document cache on low memory event
RavenDB-1307 Clear cached items in IndexSearcherHoldingState when memory is running low
Better errors
issue 2123 fix
Ensure we delete child databases
Merge branch 'RavenDb_2123' of https://github.com/ReginaBricker/ravendb

Conflicts:
	Imports/Newtonsoft.Json/Src/Newtonsoft.Json/JsonSerializer.cs
	Imports/Newtonsoft.Json/Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs
RavenDB-2252 Query.Search with SearchOptions.Not should produce expression (-Property:(value) AND Property:(*))
RavenDB-2243 Create Studio page for /debug/identities
RavenDB-2252 Query.Search with SearchOptions.Not should be wrapped in brackets
Merge branch 'RavenDB_2243' of https://github.com/ml054/ravendb
Merge branch 'RavenDB-2252' of https://github.com/ppekrol/ravendb
java tests fixed
Merge branch 'java' of https://github.com/ml054/ravendb
Use a semaphore rather than a single variable to detect when we are busy replicating another server
RavenDB-1307 Set the number of items to process to initial value in AutoTuners when available memory is very low
RavenDB-1307 Do not add future batches when the memory is running low
RavenDB-1307 Prevent triggering the event to frequent when the low memory notification object is in the signaled state