SI-7349 Partest supports test-interface

This commit updates Scalacheck to 1.10.1 and invokes it using the
test-interface API.  This obviates kludgy output checking for result
status.

As indicated in the commit message, the framework for scaladoc tests
needs a dash of sanity.  I envision that the runner will run scaladoc for
us, and the test consist of code to doc + assertions about the result.

Two smaller files are merged to reduce the number of source files named
DirectSomething or SomethingRunner.scala.  Or is it RunnerSomething.

Review by @paulp who by now wishes he hadn't touched Par-Test. Or @phaller who perhaps wishes he'd kept the name, PHaller-Test. Or Par-Hell-Test.

This PR should be rebased after https://github.com/scala/scala/pull/2385 which is a babier step. (I'll do the rebase.)