Refactor test with a view to extending it to cover bug 55331. No functional change to this point.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1509128 13f79535-47bb-0310-9956-ffa450edef68
Fix NPE in FileMessageFactory.main when specify empty file as arguments.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1509134 13f79535-47bb-0310-9956-ffa450edef68