Attach SOLR ErrorListener to backend instance, not name
Provide method to attach ErrorListener to shared event manager

* VuFind/Search/Solr/AbstractErrorListener.php (attach): New
  method. Attach to shared event manager.
Create and attach SOLR v4 error listener

* VuFind/Search/Factory/AbstractSolrBackendFactory.php
  (createListeners): Create and attach SOLR v4 error listener.
Fix SOLR Backend, E_STRICT

* VuFindSearch/Backend/Solr/Backend.php (search): Use dedicated
  variable for E_STRICT compliance.