Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=55943
Better implementation of the class loader check that prevents web applications from trying to override J2SE implementation classes.
Refactor the way a null parent class loader was handled which enables a number of null checks and object creation calls to be removed

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1559134 13f79535-47bb-0310-9956-ffa450edef68