Better Logging + error handling when a Signature Crypto instance isn't specified or cannot be loaded

git-svn-id: https://svn.apache.org/repos/asf/webservices/wss4j/trunk@1467227 13f79535-47bb-0310-9956-ffa450edef68
Compilation fix following forward-merge

git-svn-id: https://svn.apache.org/repos/asf/webservices/wss4j/trunk@1467228 13f79535-47bb-0310-9956-ffa450edef68