Edit GenericUnWrapper with test (GEOS-6578)

GenericUnWrapper implemented with method reflection, preconfigured unwrap method lookup for several JBoss environments.

https://jira.codehaus.org/browse/GEOS-6578
Guard against NPE in ResourcePool.FeatureTypeCache.dispose(...)
Fix handling of NPE in AdvancedDispatchFilter (GEOS-6529)

NullPointerExcepiton is thrown when geoserver-monitor-plugin is added to geoserver 2.5.1 and additional application-specific plugin servlets are added into geoserver.

http://jira.codehaus.org/browse/GEOS-6529