Improve testing interactive experience.

Currently the exceptions that happen in the test are swallowed, as
the JVM is forced to exit before printing the stack trace.
Also assert message doesn't contain information about the problem.

The call to "sys.exit" masks bugs in the testing framework, that
has to be addressed more elaborately, so here we remove it. Also
add the message parameter to assert to make it more informative.

After removing "sys.exit" call, doc test starts failing. I suspect
there might be a problem when expanding doc variables, but this
should be addressed separately.
Iterator.++ no longer blows the stack.

To my chagrin we still hadn't gotten this one. I took a new
approach which seems like a winner to me. Here's a benchmark:

object Test {
  def run(n: Int) = println((1 to n).foldLeft(Iterator.empty: Iterator[Int])((res, _) => res ++ Iterator(1)) sum)
  def main(args: Array[String]): Unit = run(args(0).toInt)
}

Runtime before this commit for various n:

  500   0.403 real
  1000  0.911 real
  1500  2.351 real
  2000  5.298 real
  2500 10.184 real

Runtime after this commit, same n:

  500  0.346 real
  1000 0.359 real
  1500 0.368 real
  2000 0.379 real
  2500 0.390 real

In the test case I dial it up to 100000.
SI-7302 importing from Any.

Turns out the "minor tweaks" in 632daed4ed were only minor
for major values of minor. You can indeed import members from
Any/Object, so long as you rename them. Reverted logic error.
Test case will accompany SI-7233 upon merge into master.
Merge pull request #2323 from paulp/pr/iterator_++

Iterator.++ no longer blows the stack.
Merge commit 'refs/pull/2326/head' into pr/merge-395e90a786
Merge commit '395e90a786' into pr/merge-395e90a786

* commit '395e90a786':
  SI-7251, compiler crash with $.
  SI-7240 fixes language feature lookup
  SI-7233 Account for aliased imports in Erasure
  SI-7233 Account for aliased imports in eta expansion.
  SI-7132 - don't discard Unit type in interpreter
  SI-6725 `f` interpolator now supports %n tokens

Conflicts:
	src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
	src/compiler/scala/tools/nsc/typechecker/EtaExpansion.scala
	src/repl/scala/tools/nsc/interpreter/ExprTyper.scala
Merge pull request #2333 from paulp/pr/merge-395e90a786

Merge 2.10.x (through 395e90a786) into master.
Merge pull request #2316 from vigdorchik/interactive_test_framework

Improve testing interactive experience.
Added :kind command to show kinds of types and type constructors.
Originally implemented by @eed3si9n here: https://gist.github.com/eed3si9n/3610635
Now it sees all the types, but does not correctly detect the kind.
As suggested by @xeno-by
A pretty much working copy.
Added verbose mode.
Not-working version.
A fully working version. Thanks to @xeno-by and @retronym.
Working around NoType