U.ReentrantReadWriteLockTracer improper realization.

ReentrantReadWriteLockTracer accepts ReentrantReadWriteLock as a delegate and stores delegates for readLock and writeLock. But ReentrantReadWriteLock#isWriteLockedByCurrentThread uses sync object to evaluate the result instead of writeLock, and ReentrantReadWriteLockTracer has it's own sync object.
As a result, if ReentrantReadWriteLockTracer is used to create checkpoint lock (when IGNITE_PDS_LOG_CP_READ_LOCK_HOLDERS=true), GridCacheDatabaseSharedManager#checkpointLockIsHeldByThread doesn't work correctly: it returns false when checkpoint lock is acquired.