Start thinking about a benchmark

Results from one run:

    [info] Benchmark                          (count)  (p1)  (p2)  (p3)  Mode  Cnt    Score    Error  Units
    [info] ClassMatchBenchmark.intSwitchShow    10000     1     1     1  avgt   30  393.881 ± 20.407  us/op
    [info] ClassMatchBenchmark.patmatShow       10000     1     1     1  avgt   30  459.134 ± 35.898  us/op
    [info] ClassMatchBenchmark.virtualShow      10000     1     1     1  avgt   30  314.769 ±  5.255  us/op

Add an another example of a Writer/Option monad

Don't insert null assignments for the terminal state.

Eliminate empty states

Redo ANF forced

Don't reset almost final value to true

Workaround bug in Scala runtime reflection on JDK 9

The underlying bug is tracked as scala/scala-dev#304
and blocks our SBT starting on JDK 9.

This commit avoids using the empty package in our build definition.

Remove manual mixins in JFunctionN.

These manual mixins were forwarding to the impl classes have
just been removed. We can now rely on default methods instead.

Update Tests:

 - Fix test/files/pos/t1237.scala, we can't have an outer field
   in an interface, always use the outer method.
 - Don't crash on meaningless trait early init fields
   test/files/neg/t2796.scala
 - Remove impl class relate parts of inner class test
 - Remove impl class relate parts of elidable test
 - Remove impl class related reflection test.
 - Remove test solely about trait impl classes renaming
 - Update check file with additional stub symbol error
 - Disable unstable parts of serialization test.
    - TODO explain, and reset the expectation

Fix for SI-4929. Includes (previously failing) test case.

This uses thread-local variables, which is not ideal; however, I can't
find any way to fix it otherwise that doesn't involve significant
refactoring.

Version number: 2.8.2.RC3 -> 2.8.2.final