Multiple filter-mappings for same filter with overlapping url-patterns and/or servlet-names

The Servlet Spec is unclear on how to handle multiple filter-mappings for the same filter that have overlapping url-patterns and or servlet-names.

See issue https://github.com/eclipse-ee4j/servlet-api/issues/52 and issue https://github.com/eclipse-ee4j/servlet-api/issues/318.

As described in [servlet api issue 52](https://github.com/eclipse-ee4j/servlet-api/issues/52), the current behaviour of jetty is:

> If you define a single filter mapping with multiple url-patterns \[as the example above\], we will only apply the filter once. If, however, you defined different filter mappings for each url-pattern, we would apply the filter once for each mapping. Obviously consistent behaviour would be desirable.