akka/akka — pull request #15978 by rkuhn (2014-09-24 20:13:10+00:00)
Title: +str #15977 add SourceFlow/SinkFlow

- sources must really be sources (the same for sinks), hence
ProcessorFlow cannot implement either of these
- therefore they are just other names for FlowWithSource/Sink
- also fixed type-safety of FlowGraph’s edge labels