Ticket 47781 - Server deadlock if online import started while
server is under load
Bug Description: Online import of ldif containing repl data deadlocks server.
Fix Description: Replace the replica lock(PRLock) with a PRMonitor reentrant lock.
Reviewed by: nhosoi(Thanks!)
(cherry picked from commit 0e11f7182a3b8f42f90ec8335936965b88a11336)
(cherry picked from commit 5b46542a71b1fe2cab03aa44f6f84d579f5a9683)