Fix for GRAILS-10291 "Method name must not be null" exception when using...

This is a proposed fix for Fix for GRAILS-10291 "Method name must not be null" exception when using custom onUnauthorized method in grails-shiro plugin's ShiroSecurityFilters which calls filter.forward rather than filter.redirect"

AbstractGrailsControllerHelper#handleURI needs to avoid getting the controller cached in the request to handle the forward. This couldn't be accomplished by looking for the presence of the existing "org.codehaus.groovy.grails.FORWARD_CALLED" attribute added to the request by ForwardMethod, because it is added after the call to AbstractGrailsControllerHelper#handleURI. Modifying ForwardMethod to add that attribute sooner causes other problems, such as CompositeInterceptor killing processing of the request prematurely. So the approach of this fix is for ForwardMethod to add a new attribute "org.codehaus.groovy.grails.FORWARD_IN_PROGRESS" to the request that AbstractGrailsControllerHelper#handleURI sees as an indication that it should not use the controller cached in the request.