javax.el.BeanELResolver:
- getFeatureDescriptors, getCommonPropertyType do not throw NPE when the supplied context is null.
- setValue will throw PropertyNotWritableException instead of PropertyNotFoundException when there is no setter for the property.
- unit test is added

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1517536 13f79535-47bb-0310-9956-ffa450edef68