Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56016
When loading resources for XML schema validation, take account of the possibility that servlet-api.jar and jsp-api.jar may not be loaded by the same class loader.
Patch by Juan Carlos Estibariz.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1558894 13f79535-47bb-0310-9956-ffa450edef68