OAK-1329: Relaxed JCR locking behavior

Setting the oak.relaxed-locking session attribute to true enables
the relaxed locking rules that allow a session to unlock a lock owned
by the current user without first explicitly acquiring the relevant
lock token.

This is a convenience feature without security implications as we already
expose the lock token through Lock.getLockToken() to all sessions of the
user who owns the lock. Thus in practice this feature just removes the
need to do lockManager.addLockToken(node.getLock().getLockToken())
before unlocking a node with node.unlock().

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1581696 13f79535-47bb-0310-9956-ffa450edef68