SI-7757 disallow constructor annotations on traits

Previously it was possible to define constructor annotations on traits
with really weird side-effects (parser lost the body of the trait). Now
constructor annotations on traits will cause appropriate syntax errors.
SI-7757 add additional test case with annotation on the next line
SI-7756 Uncripple refchecks in case bodies

In 65340ed4ad2e, parts of RefChecks were disabled when
we traversed into the results of the new pattern matcher.
Similar logic existed for the old pattern matcher, but in
that case the Match / CaseDef nodes still existed in the tree.

The new approach was too broad: important checks no longer
scrutinized the body of cases.

This commit turns the checks back on when it finds the remnants
of a case body, which appears as an application to a label def.
SI-6797 Test case for already-fixed DelayedInit bug

Progressed in b4fbb7be0e2, "translation for DelayedInit keeps
more code in original class."
SI-7729 Fix broken windows build

Fixing #ifdiff uncovered a latent bug in partest when it detects
paths to normalize in test log output.  It would not normalize
file separators for test names with non-word characters.

This commit normalizes the test name to the ticket number as a
workaround until the next partest version is picked up.

It also fixes partest in this repo in case we've not yet switched
over to the new repo.  A separate PR will be submitted to the new
repo as necessary.
Merge pull request #2839 from densh/topic/si-7757

SI-7757 disallow constructor annotations on traits
Merge pull request #2854 from som-snytt/issue/7729-slash

SI-7729 Fix broken windows build
Merge pull request #2840 from retronym/ticket/7756-2.11

SI-7756 Uncripple refchecks in case bodies
Merge pull request #2853 from retronym/ticket/6797

SI-6797 Test case for already-fixed DelayedInit bug
Move partest to https://github.com/scala/scala-partest

As partest is now resolved from maven, `test/partest` uses `ant test.suite.init`
to determine the classpath (serialized to build/pack/partest.properties)
that's necessary to run `scala.tools.partest.nest.ConsoleRunner`.

Thus, partest gets exactly the same classpath, whether run from
the command line through `test/partest` or via `ant test`.

The version of partest we're using is specified by
properties defined in versions.properties (formerly `starr.number`).

Currently, we're using:

```
scala.binary.version=2.11.0-M4
partest.version.number=1.0-RC3
```

NOTES:
  - The version of Scala being tested must be backwards binary compatible with
    the version of Scala that was used to compile partest.
  - Once 2.11 goes final, `scala.binary.version=2.11`, and `starr.version=2.11.0`.
  - Need scalacheck on classpath for test/partest scalacheck tests.
  - Removed atrophied ant tests (haven't been run/changed for at least two years
    I checked 81d659141a as a "random" sample).
  - Removed scalacheck. It's resolved as a partest dependency.
  - For now, use a locally built scalap
  - Kept the trace macro in the main repo (partest-extras)
  - New targets for faster pr validation: test-core-opt, test-stab-opt