Random wartremover and lint cleanups

Lots of minor tweaks based on -Xlint and enabling wartremover.

I would like to switch -Xlint on permently but it falls over on some of the akka code (inference of any).
I'll add comments on the various changes so you can see what they are based on.
This is an interesting one - put only takes a single argument, so scala infers an extra set - lint objects