Ticket 47927: Uniqueness plugin: should allow to exclude some subtrees from its scope
    
    Bug Description:
    	Support excluding subtrees in uniqueness plugin
    
    Fix Description:
    	Exclude subtrees from uniqueness check if they are specified in the
    	plugin config.
    
    	To exclude certain parts of the tree from uniqueness check,
    	set
    	    uniqueness-exclude-subtrees: cn=subtree,dc=example,dc=com
    	in the plugin's configuration.
    
    	Only new style configuration is supported for specifying excludes.
    
    https://fedorahosted.org/389/ticket/47927
    
    Reviewed by: Rich (thanks !)
    
    Platforms tested: F17
    
    Flag Day: no
    
    Doc impact: yes (new uniqueness attribute uniqueness-exclude-subtrees)