Move more code into src/interactive.

Moved more code which is only used by the presentation compiler.
It's hard to move code in that direction because the compiler
is lower in the dependency chain, so it would be great if the
IDE would sign off on moving it. (I doubt it has other users.)

  scala/tools/nsc/interactive/BrowsingLoaders.scala
  scala/tools/nsc/interactive/Lexer.scala
  scala/tools/nsc/interactive/MultiHashMap.scala
  scala/tools/nsc/interactive/Pickler.scala
  scala/tools/nsc/interactive/PrettyWriter.scala
  scala/tools/nsc/interactive/Replayer.scala