SI-7269 Rework MapLike#retains to account for desugaring change

`MapLike#retains` contains a for-comprehension that relied on the strict
`filter` by its generator. You can't, in general, iterate a mutable map
and remove items in the same pass.

Here's the history of the desugaring of:

    def retain[A, B](thiz: mutable.Map[A, B])(p: (A, B) => Boolean): thiz.type = {
      thiz.foreach {
        case (k, v) =>
          if (p(k, v)) thiz -= k
      }

Before regression (c82ecabad6~1):

    thiz.filter(((check$ifrefutable$1) => check$ifrefutable$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => true
       case _ => false
    })).withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

After regression (c82ecabad6, which incorrectly assumed in the parser that
no filter is required for isInstanceOf[Tuple2])

    thiz.withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
      case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

After the reversion of c82ecabad6, v2.10.2
This is also after 365bb2b4e, which uses `withFilter` rather than `filter`.

    thiz.withFilter(((check$q$1) => check$ifrefutable$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => true
       case _ => false
    })).withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
      case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

This commit does the same as `SetLike#retains`, and converts the map to
an immutable list before the rest of the operation.
[nomaster] SI-7652 Bad tools fails loudly

A brief message is all that's required to
alleviate the look of consternation on the
face of your user.
[nomaster] SI-7652 REPL extended quest for tools

Javap tries harder and fails louder when
looking for tools.jar

This is a backport of the method as it
was first coded for partest.

If JAVA_HOME is wrong, it will either
fail with a message or succeed after
rooting about.

```
apm@mara:~/tmp/q$ JAVA_HOME=$JAVA7_HOME JAVACMD='/usr/lib/jvm/java-6-openjdk-amd64/bin/java' /home/apm/projects/snytt/build/pack/bin/scala
Welcome to Scala version 2.10.3-20130829-123337-59d6568daa (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :javap
:javap [-lcsvp] [path1 path2 ...]

scala> :javap java.lang.Object
Failed: Could not load javap tool. Check that JAVA_HOME is correct.

apm@mara:~/tmp/q$ JAVA_HOME=/usr/lib/jvm/java-6-openjdk-amd64/jre JAVACMD='/usr/lib/jvm/java-6-openjdk-amd64/bin/java' /home/apm/projects/snytt/build/pack/bin/scala
Welcome to Scala version 2.10.3-20130829-123337-59d6568daa (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala>

scala> :javap
:javap [-lcsvp] [path1 path2 ...]

scala> :javap java.lang.Object
Compiled from "Object.java"
```
SI-7814 Avoid init cycle between Predef, `package`, ScalaRuntime

Not every application will force these in a single thread; we
have to do our best to avoid cycles between them.

The enclosed test was failing every time before the change.

This commit breaks the cycle by avoiding computing `tupleNames`
in the constructor of `ScalaRuntime`. The new version has the
added benefit of including specialized tuple subclasses, which
is verified with a unit test for `isTuple`.

Are there more of these lurking? It seems likely. I'm more than
a little concerned about the way the `ControlThrowable` fires up
`scala.SystemProperties` to check whether or not to suppress
stack traces; there is already an ugly hack in place:

    object NoStackTrace {
      final def noSuppression = _noSuppression

      // two-stage init to make checkinit happy,
      // since sys.SystemProperties.noTraceSupression.value
      // calls back into NoStackTrace.noSuppression
      final private var _noSuppression = false
      _noSuppression = sys.SystemProperties.noTraceSupression.value
    }
SI-7814 Updates the instrumented version of ScalaRuntime.

Some tests for specialization use a modified version of
the standard library that count boxing, array lookups etc.

These sources are updated manually with the script:

    % test/instrumented/mkinstrumented.sh build

Looks that that wasn't done for a while, though.

This commit brings it up to date, and adjusts a few braces in
ScalaRuntime.scala so the patch srt.scala (used by that script)
is shorter.

We should really avoid checking in the products of that script and
run it as part of the build, or, better, use the bytecode
instrumentation framework instead of a modified standard library.
But I have to leave that for another day.
SI-7818 Cast our way out of extended existential angst

`substituteSymbols` is not sophisticated enough to
operate on `TypeSkolem`-s which are based on one of the
"from" symbols.

The pertinant usage of `substituteSymbols` for this bug in
in `Extender`. Recapping on that transform:

    // orig
    class C[T](...) extends AnyVal { def foo[U] = <rhs> }

    // transform
    class C[T] extends AnyVal { ... }
    object C  { def foo$extension[T', U'] = <rhs'> }

Where `<rhs'>` has been subtituted with, among other things,
`[T, U] ~> [T', U']`.

In this case our expected type contains a new type parameter
(of the extension method), whereas the type of the RHS contains
an existential skolem still pinned to the corresponding class type
parameter.

    tree.tpe         = Observable1#7037[_$1#12344]
    <_$1#12344>.info =  <: T#7040
    pt               = Observable1#7037[T#15644]

The limitation of substution is lamented in the comments
of `adaptMismatchedSkolems`, which faces the harder version of
the issue where the skolems are in the expected type.

But, we're in the "easy" case with the skolems in the tree's type;
we can cast our way out of the problem.

See also f335e447 / ed915c54.
Merge pull request #2895 from som-snytt/issue/7652-tools-jar-backport

SI-7652 REPL tools jar backport
SI-7767 avoid rejecting Scaladoc comments in early initializers

review by @retronym
SI-7767 Test case for Scaladoc on early initializers
Merge pull request #1 from retronym/ticket/7767-test

Test case for SI-7767
Merge pull request #2911 from retronym/ticket/7814

SI-7814 Avoid init cycle between Predef, `package`, ScalaRuntime
Merge pull request #2866 from retronym/ticket/7269

SI-7269 Rework MapLike#retains to account for desugaring change
Merge pull request #2922 from huitseeker/issue/7767

SI-7767 avoid rejecting Scaladoc comments in early initializers
Merge pull request #2916 from retronym/ticket/7818

SI-7818 Cast our way out of extended existential angst
Merge commit '7fa0e60' into merge/2.10.x-to-master

    git merge -s ours 7fa0e60
Merge remote-tracking branch 'origin/2.10.x' into merge/2.10.x-to-master

Conflicts:
	src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
Build partest-extras under `pack.done`

... rather than just in `test.suite.init`.

Now:

	% ant pack.done | egrep -i 'compiling|jar'
	desired.jars.uptodate:
	[quick.partest-extras] Compiling 1 file to /Users/jason/code/scala/build/quick/classes/partest-extras
	      [jar] Building jar: /Users/jason/code/scala/build/pack/lib/scala-partest-extras.jar

Note: Because of the recent changes to the way that the classpath
or partest is build up (it is done via `ant test.suite.init`), partest
no longer works with quick/classes, the classpath is always taken as
`pack`. So `ant quick.bin && ./test/partest` is insufficient; you need
to run `ant pack.done`, or just `ant` if you prefer brevity.
Merge remote-tracking branch 'origin/master' into merge/2.10.x-to-master

Conflicts:
	src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
Merge pull request #2928 from retronym/merge/2.10.x-to-master

merge 2.10.x to master