SOLR-4249: UniqFieldsUpdateProcessorFactory now extends FieldMutatingUpdateProcessorFactory and supports all of it's selector options (merge r1518717)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1518746 13f79535-47bb-0310-9956-ffa450edef68