Checkpoint commit for OPENDJ-1206 : Create a new ReplicationBackend/ChangelogBackend 
 to support cn=changelog
CR-4052

Preparatory work for the changelog backend: make the "Changelog Exchange Control"
 available to the backend when search(SearchOperation) method is called 

* LocalBackendSearchOperation#handleRequestControls() method:
   handle the "Changelog Exchange Control" : add it to the SearchOperation 
   if provided in the request

* SearchOperation, SearchOperationBasis and SearchOperationWrapper classes:
   add getter and setter for the "Changelog Exchange Control" (ECLRequestControl class)

* core.properties : add new message for case when  "Changelog Exchange Control" is requested
 but not supported by a backend