Fix maven release artifacts download script to download exactly what's under lucene/maven/ and solr/maven/ at the RC URL - previously the top-level 'org/apache/' directories were not being output.  Also, document the wget options used.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1626594 13f79535-47bb-0310-9956-ffa450edef68