LUCENE-5761: upgrade note for solr (merge r1603227)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_9@1603229 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6175: Merged test fixes from branch_4x

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_9@1603242 13f79535-47bb-0310-9956-ffa450edef68