create new params object for each shard request to prevent concurrent modification exception when SolrJ modifies the params

git-svn-id: https://svn.apache.org/repos/asf/lucene/solr/trunk@666876 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/solr/handler/component/SearchHandler.java

@@ -209,7 +209,7 @@ public class SearchHandler extends RequestHandlerBase implements SolrCoreAware
 
             // TODO: map from shard to address[]
             for (String shard : sreq.actualShards) {
-              ModifiableSolrParams params = sreq.params;
+              ModifiableSolrParams params = new ModifiableSolrParams(sreq.params);
               params.remove("shards");      // not a top-level request
               params.remove("indent");
               params.remove("echoParams");