MIME4J-241: inconsistent StringInputStream read zero behavior

git-svn-id: https://svn.apache.org/repos/asf/james/mime4j/trunk@1606057 13f79535-47bb-0310-9956-ffa450edef68
Added builder class for Message instances

git-svn-id: https://svn.apache.org/repos/asf/james/mime4j/trunk@1606062 13f79535-47bb-0310-9956-ffa450edef68