SBT 0.13 build
Remove classes specific to scala/scala

We don't want to depend on scala.tools.asm nor the repl here.
The next commit refactors partest's classpath handling,
so that we can build the files we remove here in the compiler build,
and include the resulting artifacts on the classpath there.
remove SBTRunner -- AntRunner will suffice
Simplify classpath handling a bit.

It's still utter madness, so -- for an extra sanity check --
I'm printing the banner for every test run.

The classpath used for tests (modulo additions for certain test cases)
is `fileManager.testClassPath` (or `testClassPathUrls`).

Ideally, we should get rid of all this custom logic in FileManager,
and just use COMPILATION_CLASSPATH.
less mutation, interface without scala dependencies

  - Initialize FileManager in one go, instead of with lots of mutations.
  - To allow calling partest reflectively from sbt's test interface,
    make signature of AntRunner pure Java.
formatting
sbt runner
sbt runner needs test-interface
allow versioned jars for scala-library etc by looking only at prefix
make fileManager lazy to avoid NPE
formatting
WIP that shows where classpath handling must change