Improving required signed elements detection


Conflicts:
	src/main/java/org/apache/ws/security/util/WSSecurityUtil.java

git-svn-id: https://svn.apache.org/repos/asf/webservices/wss4j/branches/1_6_x-fixes@1619368 13f79535-47bb-0310-9956-ffa450edef68