Fixed issue #2269: unlock database files during backup
Minor: added log on lock, unlock of storage files
Distributed: fixed minor issues on replication
Minor: added check for NULL record
Added replication test case
Fixed #2271. Remove System.out.println from production code.
Minor: refactoring
Fixed issue #2267 about functions without params
Issue #1892 support for null keys for primitive values was added.
 All index range methods with exception of cursors were removed.
 Tx support for range query methods was added.
Tests: improved multi-thread tests base class and provided MT graph test
Merge branch 'develop' of https://github.com/orientechnologies/orientdb into develop
Test: Added usage of index in graph speed tests
Distributed: Fixed problem on start up
Distributed: temporary revertes management of maxOfflineMessages
Issue #1892 failed tests were fixed.
Merge remote-tracking branch 'origin/develop' into develop
Fixed #2266. Management of serializers for SBTree
Minor: remove unnecessary operations from SBTreeBonsai.create()
Distributed: fixed management of queues
Fixed #2266. Management of serializers for SBTree