Allow containment features for connections

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see https://groups.google.com/forum/#!topic/spray-users/rxrOpVLVn4A

Currently containment features are filtered out in scoping - we have to check 
which side effects it would produce if we would allow those.

Maybe also related to 
http://code.google.com/a/eclipselabs.org/p/spray/issues/detail?id=235 

Original issue reported on code.google.com by de.abg.r...@gmail.com on 14 Jul 2013 at 3:32