Add counters to File#{exists, isFile, isDirectory}.

Due to limitations in the Statistics machinery, these are only
reported if this patch is applied.

        --- a/src/reflect/scala/reflect/internal/util/Statistics.scala
        +++ b/src/reflect/scala/reflect/internal/util/Statistics.scala
        @@ -109,7 +109,7 @@ quant)
            *  Quantities with non-empty prefix are printed in the statistics info.
            */
           trait Quantity {
        -    if (enabled && prefix.nonEmpty) {
        +    if (prefix.nonEmpty) {
               val key = s"${if (underlying != this) underlying.prefix else ""}/$prefix"
               qs(key) = this
             }
        @@ -243,7 +243,7 @@ quant)
            *
            *  to remove all Statistics code from build
            */
        -  final val canEnable = _enabled
        +  final val canEnable = true // _enabled
Optimization: avoid isDirectory call in DirectoryClassPath traversal

If we just established that the given path is a File or a Directory,
we don't need to go straight back to disk to re-check.

Background: When profiling an application that was using the interpreter
to compile a script, a lot of time was reported in exists / isDirectory
/ isFile. For the record, I happened to be profiling on Windows.

Turns out some of these calls are redundant, this commit and the
subsequent eliminate two sources thereof.

Here's an example of how it helps:

Taking a Hello, Akka! application, and compiling it with the compiler
and library on a directory classpath (ie, using build/quick):

    class HelloActor extends Actor {
      def receive = {
        case "hello" => println("hello back at you")
        case _       => println("huh?")
      }
    }

    object Main extends App {
      val system = ActorSystem("HelloSystem")
      // default Actor constructor
      val helloActor = system.actorOf(Props[HelloActor], name = "helloactor")
      helloActor ! "hello"
      helloActor ! "buenos dias"
    }

    % qbin/scalac -Ystatistics -classpath ~/.ivy2/cache/com.typesafe.akka/akka-actor_2.10/jars/akka-actor_2.10-2.1.1.jar:/Users/jason/.ivy2/cache/com.typesafe/config/bundles/config-1.0.0.jar sandbox/test.scala 2>&1 | grep File

Before
----------------------------------
File.isFile calls           : 7620
File.isDirectory calls      : 8348
File.exists calls           : 5770

After
----------------------------------
File.isFile calls           : 7620
File.isDirectory calls      : 2319
File.exists calls           : 5770
Optimization: avoid call to exists in PlainFile#iterator

If we just established that the given path is a File or a Directory,
we can assume it continues to exist.

Before
----------------------------------
File.isFile calls           : 7620
File.isDirectory calls      : 2319
File.exists calls           : 5770

After
----------------------------------
File.isFile calls           : 7620
File.isDirectory calls      : 2319
File.exists calls           : 345
SI-7312 @deprecatedInheritance now ignores same-file subclasses

This allows us to deprecate external inheritances as a prelude
to sealing a class, without enduring the warnings ourselved in
interlude.
SI-7315 Test @deprecatedInheritance / @specialized interplay

Don't warn about the specialized subclass.

Fixed in the previous commit for a similar issue SI-7312.
SI-7335 Mandate that parents of Predef must be defined in Predef.scala

This avoids thorny issues of cyclic references and/or missing symbol errors
due to the way Predef is completed earlier than user classes, and due to the
addition of `import Predef._` to LowPriorityImplicits.scala. More details in
Lukas's comments in [2].

How did we bootstrap originally? Manually ordering source files,
either in the Ant Build [1], or later in Global [2]. But neither mechanism
remains in place (due, I suppose, to the difficulty in defending them
with a test case.) The reordering in Global was removed in [3].

After the change, we can compile the standard library without the
results of a prior compilation run on the classpath.

    rm -rf target/locker/library/classes/scala && export LIB=build/pack/lib; java -Xmx1G -cp $LIB/scala-library.jar:$LIB/scala-reflect.jar:$LIB/scala-compiler.jar:$LIB/forkjoin.jar scala.tools.nsc.Main @args.txt
    src/library/scala/SerialVersionUID.scala:15: warning: Implementation restriction: subclassing Classfile does not
    make your annotation visible at runtime.  If that is what
    you want, you must write the annotation class in Java.
    class SerialVersionUID(value: Long) extends scala.annotation.ClassfileAnnotation
          ^
    warning: there were 75 deprecation warning(s); re-run with -deprecation for details
    warning: there were 1 unchecked warning(s); re-run with -unchecked for details
    warning: there were 5 feature warning(s); re-run with -feature for details
    four warnings found

 Where @args.txt contains:

     -classpath
     lib/forkjoin.jar:target/locker/library/classes
     -sourcepath
     src/library
     -d
     target/locker/library/classes
     src/library/scala/Function3.scala
     src/library/scala/Console.scala
     <more of src/library/**, unsorted>

This change will break scala-virtualized, which will need to move
the contents of StandardEmbeddings.scala into Predef.scala.

[1] https://github.com/scala/scala/commit/c5441dc
[2] https://github.com/scala/scala/commit/e72f0c7
[3] https://github.com/scala/scala/pull/968
SI-7335 Don't import Predef._ in Predef.scala

The check for this was foiled by the introduction of
DeprecatedPredef in c26a8db0. This didn't cause any
harm, but in any case this commit restores the intended
state of affairs.

The change is visible only through logging; no test case
is included.

    qbin/scalac -Ydebug -Ylog:all src/library/scala/Predef.scala -Ystop-after:typer 2>&1 | grep -i "Omitted import of Predef"
    [log namer] Omitted import of Predef._ for Predef.scala
    [log typer] Omitted import of Predef._ for Predef.scala

A redundant override of `firstDefinesClassOrObject` is also
removed.

Maybe we can remove the special case altogether?
SI-7335 Add logging for a now-impossible* case in Symbol#exists.

* Impossible (to the best of my knowledge) because LowPriorityImplicits
is now defined in Predef.scala. Were I more sure, we could trip an
assertion here, rather than the devWarning.
SI-7335 Sharpen up comment about implicit prioritization.
Reifier -> AST Node test.

It's a Node-by-Node tour of the reifier's abilities and
occasional foibles.

That is one spectacularly attractive checkfile.
Merge pull request #2335 from retronym/topic/opt-file-access

Optimize file metadata access
SI-7335 Remove special case for import of Predef._ in Predef.scala

Perhaps this once was problematic, but in our modern age we can
bootstrap perfectly well with this import.
Merge remote-tracking branch 'origin/2.10.x' into merge/v2.10.1-235-g4525e92-to-master

Conflicts:
	bincompat-backward.whitelist.conf
	bincompat-forward.whitelist.conf
	src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
	src/compiler/scala/tools/nsc/typechecker/Typers.scala
	src/reflect/scala/reflect/internal/Types.scala
Merge pull request #2391 from retronym/merge/v2.10.1-235-g4525e92-to-master

Merge/v2.10.1 235 g4525e92 to master
Merge pull request #2368 from retronym/ticket/7335

SI-7335 Simpler bootstrapping the standard library
Merge pull request #2336 from retronym/topic/deprecated-inheritance-tweak

SI-7312 @deprecatedInheritance now ignores same-file subclasses
Merge pull request #2380 from paulp/pr/reifier-ast-test

Reifier -> AST Node test.
SI-6775 Racy synchronization of specialized methods.

When the new specialized method is created that overrides a method
in a base class, cloneSymbol is called on a base method, rather than
on a non-specialized overrider.

This results in flags incorrectly (un)set on the clone, which include,
among others, SYNCHRONIZED snd FINAL.

To fix the problem, we don't forward to specializedOverload, but
rather clone overriding method directly.