issue 1804 : Ensure that conflicts are visible to administrators

The replication monitoring information already provides the
attribute unresolved-naming-conflicts that counts the number of conflicts
that was not automatically resolved since last startup.

The conflicting entries are also marked with the ds-sync-confict attribute
so that administrators can look for these entries 
using filter ds-sync-confict=*

This code add the generation of an administrative alert when a conflict is
detected so that administrators can be made aware of the problem.