Move some code from s.t.n.io to s.t.n.interactive

The only usages of scala.tools.nsc.io.{Lexer,Pickler,PrettyWriter,
Replayer} can be found in scala.tools.nsc.interactive.

Let's move those files closer to their dependencies.
Merge pull request #2687 from soc/topic/io-to-interactive

Move some code from s.t.n.io to s.t.n.interactive