Don't crash if cpsParam is not on the classpath.

When checking if a piece of code needs the continuations plugin, the cpsParam classes may not be on the class path. Assume it does not need it in that case.
SI-5617 Better error message for "x overrides nothing".

"It looks like you're trying to override a method", notes Clippy.
SI-4842 Forbid access to in-construction this in self-constructor args

The check was already in place for direct calls to the super constructor.
Without this additional check, ExplicitOuter crashes, as it doesn't create
an $outer pointer for the constructor-arg scoped inner object, but expects
one to exist when transforming the Outer.this reference.
Updated scalacheck sources.

To current scalacheck head 7ffda752d8 except for this diff:

diff -rw src/scalacheck/org/scalacheck/Arbitrary.scala /s/scalacheck/src/main/scala/org/scalacheck/Arbitrary.scala
13d12
< import scala.reflect.ClassTag
281c280
<   implicit def arbArray[T](implicit a: Arbitrary[T], c: ClassTag[T]
---
>   implicit def arbArray[T](implicit a: Arbitrary[T], c: ClassManifest[T]
diff -rw src/scalacheck/org/scalacheck/Prop.scala /s/scalacheck/src/main/scala/org/scalacheck/Prop.scala
63c63
<   def mainCallsExit = false
---
>   def mainCallsExit = true
Only in /s/scalacheck/src/main/scala/org/scalacheck: ScalaCheckFramework.scala
diff -rw src/scalacheck/org/scalacheck/util/Buildable.scala /s/scalacheck/src/main/scala/org/scalacheck/util/Buildable.scala
13d12
< import scala.reflect.ClassTag
34c33
<   implicit def buildableArray[T](implicit cm: ClassTag[T]) =
---
>   implicit def buildableArray[T](implicit cm: ClassManifest[T]) =
Fix for SI-5953, extension methods crasher.

As usual, .tpe -> .tpeHK. As a side note following an old theme,
if symbols of type parameters knew that they were symbols of type
parameters, they could call tpeHK themselves rather than every call
site having to do it. It's the operation which injects dummies which
should require explicit programmer action, not the operation which
faithfully reproduces the unapplied type. Were it that way, errors could
be caught much more quickly via ill-kindedness.

Seems like an improvement over lurking compiler crashes at every call
to tparam.tpe.
Merge pull request #750 from paulp/issue/5953

Fix for SI-5953, extension methods crasher.
Making Actor Migration Tests deterministic.

Review by: @phaller
Merge pull request #711 from dragos/issue/no-crash-missing-cpsParam

Don't crash if cpsParam is not on the classpath.
Merge pull request #731 from retronym/ticket/5617

SI-5617 Better error message for "x overrides nothing".
Merge pull request #735 from retronym/ticket/4842-2

SI-4842 Forbid access to in-construction this in self-constructor args
Merge pull request #748 from jsuereth/update-scalacheck-source

Updated scalacheck sources.
Merge pull request #753 from vjovanov/actor-tests-fix

Making Actor Migration Tests deterministic.
Merge branch 'master' into prime

* master:
  Making Actor Migration Tests deterministic.
  Fix for SI-5953, extension methods crasher.
  Updated scalacheck sources.
  SI-4842 Forbid access to in-construction this in self-constructor args
  SI-5617 Better error message for "x overrides nothing".
  Don't crash if cpsParam is not on the classpath.

Conflicts:
	src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
	src/continuations/plugin/scala/tools/selectivecps/CPSAnnotationChecker.scala
	src/scalacheck/org/scalacheck/Arbitrary.scala
	src/scalacheck/org/scalacheck/Arg.scala
	src/scalacheck/org/scalacheck/Commands.scala
	src/scalacheck/org/scalacheck/ConsoleReporter.scala
	src/scalacheck/org/scalacheck/Gen.scala
	src/scalacheck/org/scalacheck/Pretty.scala
	src/scalacheck/org/scalacheck/Prop.scala
	src/scalacheck/org/scalacheck/Properties.scala
	src/scalacheck/org/scalacheck/Shrink.scala
	src/scalacheck/org/scalacheck/Test.scala
	src/scalacheck/org/scalacheck/util/Buildable.scala
	src/scalacheck/org/scalacheck/util/CmdLineParser.scala
	src/scalacheck/org/scalacheck/util/FreqMap.scala
	src/scalacheck/org/scalacheck/util/StdRand.scala
Removed any2stringadd.

This entailed inserting ""+ a handful of places and adding a few more
specific implicits to save me from creating any more latent merge pain.
Contrasting this one-time cost with the amount of pain inflicted by
any2stringadd over the years, and I have come out ahead by approximately
999,997 miles.

Also removed gratuitous StringFormat and corresponding implicit.
Removed Ensuring and made ArrowAssoc an implicit class.
Turned ArrayOps classes into implicit value classes.
New starr based on fa4218cd1c .