adding activate-mongo-async breaks jetty servlet

[aardelean]

Checkout https://github.com/aardelean/angular-akka/tree/Mongo branch. From master branch, all works fine. When I add activate-mongo-async in sbt, jetty refuses all requests with
jetty IllegalStateException: !asyncSupported error

[fwbrasil]

@aardelean Could you send the complete stack trace?