Simplify type bounds.

I started out looking to limit the noise from empty type
bounds, i.e. the endless repetition of

  class A[T >: _root_.scala.Nothing <: _root_.scala.Any]

This led me to be reminded of all the unnecessary and
in fact damaging overreaches which are performed during parsing.
Why should a type parameter for which no bounds are
specified be immediately encoded with this giant tree:

  TypeBounds(
    Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Nothing),
    Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Any)
  )

...which must then be manually recognized as empty type bounds?
Truly, this is madness.

 - It deftly eliminates the possibility of recognizing
   whether the user wrote "class A[T]" or "class A[T >: Nothing]"
   or "class A[T <: Any]" or specified both bounds. The fact
   that these work out the same internally does not imply the
   information should be exterminated even before parsing completes.
 - It burdens everyone who must recognize type bounds trees,
   such as this author
 - It is far less efficient than the obvious encoding
 - It offers literally no advantage whatsoever

Encode empty type bounds as

  TypeBounds(EmptyTree, EmptyTree)

What could be simpler.
Par-Test allows redefinition of srcDir by Ant

Since srcDir is no longer used to extract the test kind from any
given test path, it is especially benign to rely on the defness
of srcDir in order to allow redefinition during an Ant run.

The parameter is configured via the partest.srcdir property.

Maybe the keyword should be def for definite values and
red for redefinable values and ind for indefinite values.
And ded for dedefinable values optionally reset to None.
Reverting changes to AnyVals generated classes in 9a82fc0

 - Since the generator was not changed, the classes no longer represent the generated versions
SI-6898 Document AnyVal box and unbox implemention by BoxesRunTime

  - Added @boxRunTimeDoc@ and @unboxRunTimeDoc@ tokens to AnyVals
  - Doc comments refer to BoxesRunTime.java in the Scala repo
  - No comment for Unit
SI-7408 Fix test by sorting results of getDeclaredClasses

run/t4023 can fail (and has already) because the order of elements
in the reflection API is not specified and can differ between platforms
(e. g. HotSpot and Avian) or even versions (Java 7 vs. Java 8).
Merge pull request #2433 from soc/SI-7408

SI-7408 Fix test by sorting results of getDeclaredClasses
Merge pull request #2417 from paulp/pr/empty-type-bounds

Simplify type bounds.
Merge pull request #2284 from demobox/add-box-unbox-doc-comment

SI-6898 Document AnyVal box and unbox implemention by BoxesRunTime
Disabled failing bitset test.

It's a couple orders of magnitude out of whack when a test
demands a gigabyte of memory to pass. We might need to start
collecting per-test stats to avoid this kind of thing in the
future. It's a huge waste of time.
Merge pull request #2438 from paulp/pr/bitset-test

Disabled failing bitset test.
SI-7402 List extends Serializable

While we are all aware of the issues around Serialization,
I think in this case it is perfectly sound and safe to make
List serializable:

- List is not an interface, it is the base type of an ADT.
  Common behavior of its members should be reflected in the base type.
- List is sealed, there is no chance of an user providing a new
  non-serializable subtype of List.
Merge pull request #2431 from som-snytt/issue/partest-srcdir

Par-Test allows redefinition of srcDir by Ant
Merge pull request #2441 from soc/SI-7402

SI-7402 List extends Serializable