Version 2.8.7

Fixed a bug with copy-fields:
When a solr-config file contained some add-copy-field instruction, the solr instance might end up with several identical copy rules. We now apply the sanity checking that we also apply for the other Solr schema API rules for copy-field-rules: If a copy-field rule for a given source field already exists, no additional rule is added for the same field. (If you want to replace an existing copy rule, you should delete the rule first and the add the new rule, as the Solr schema API does not provide a replace operation for copy rules, as it does for the other schema operations.)