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.
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 - Since the generator was not changed, the classes no longer represent the generated versions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