Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=54497
Make error handling more robust so an error in the leak detection code doesn't prevent the Context from stopping unless the error is fatal to the JVM

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1441430 13f79535-47bb-0310-9956-ffa450edef68