SI-7391 Always use ForkJoin in Scala actors on ...
... Java 6 and above (except when the porperty
actors.enableForkJoin says otherwise)

Like SI-7236 and SI-7237, the logic in
scala.actors.scheduler.ThreadPoolConfig.useForkJoin
(which resulted in a different thread pool implementation
being chosen) was causing random hangs in the test
concurrent-stream.scala when running on Avian.
SI-6138 Centralize and refine detection of `getClass` calls

`getClass` is special cased in the compiler; this is described
in in the comments on `Definitions.Any_getClass`.

Part of this happens in `Typer#stabilize`. This was trying to determine
if an Ident or Select node was a call to `getClass` by merits of the name
of the tree's symbol and by checking that the its type (if it was a
MethodType or PolyType) had no parameters in the primary parameter list.

Overloaded user defined `getClass` methods confused this check. In the
enclosed test case, the tree `definitions.this.getClass` had an
`OverloadedType`, and such types always report an empty list of `params`.

This commit:

  - changes `stabilize` to use `isGetClass`, rather than the
    homebrew check
  - changes `isGetClass` to consider a `Set[Symbol]` containing all
    `getClass` variants. This moves some similar code from `Erasure`
    to `Definitions`
  - keeps a fast negative path in `isGetClass` based on the symbol's name
Merge pull request #2570 from soc/SI-7391

SI-7391 Always use ForkJoin in Scala actors on ...
Merge pull request #2578 from retronym/ticket/6138

SI-6138 Centralize and refine detection of `getClass` calls
SI-7375 ClassTag for value class aliases

reifyRuntimeClass now always dealiases its argument prior to processing.
Merge pull request #2619 from scalamacros/ticket/7375

SI-7375 ClassTag for value class aliases