Disallow doc type declarations when secure validation is enabled


Conflicts:
	src/main/java/org/apache/xml/security/c14n/Canonicalizer.java

git-svn-id: https://svn.apache.org/repos/asf/santuario/xml-security-java/branches/1.5.x-fixes@1537956 13f79535-47bb-0310-9956-ffa450edef68