Noise reduction + minor enhance in TreeCheckers.

Misc irrelevant work, which I can only offer as-is. It lowers
the noise in -Ycheck:* output and performs some common sense
chillaxes like not screaming ERROR IN INTERNAL CHECKING! WE'RE
ALL GOING TO DIE! when a tree doesn't hit all nine points at
the Jiffy Tree.

You can see some reasonably well reduced symbol flailing if
you run the included pending tests:

  test/partest --show-diff test/pending/pos/treecheckers

Example output,

Out of scope symbol reference {
      tree  TypeTree             Factory[Traversable]
  position  OffsetPosition       test/pending/pos/treecheckers/c5.scala:3
  with sym  ClassSymbol          Factory: Factory[CC]
   and tpe  ClassArgsTypeRef     Factory[Traversable]
   encl(1)  ModuleSymbol         object Test5
    ref to  AbstractTypeSymbol   X (<deferred> <param>)
}

7 files changed, 38 insertions, 0 deletions

diff --git a/test/pending/pos/treecheckers.flags b/test/pending/pos/treecheckers.flags
new file mode 100644
index 0000000000..5319681590
--- /dev/null
+++ b/test/pending/pos/treecheckers.flags
@@ -0,0 +1 @@
+-Ycheck:all
\ No newline at end of file
diff --git a/test/pending/pos/treecheckers/c1.scala b/test/pending/pos/treecheckers/c1.scala
new file mode 100644
index 0000000000..b936839039
--- /dev/null
+++ b/test/pending/pos/treecheckers/c1.scala
@@ -0,0 +1,12 @@
+object Test1 {
+  def f[T](xs: Array[T]): Array[T] = xs match { case xs => xs }
+  // [check: patmat] The symbol, tpe or info of tree `(x) : Array[T]` refers to a out-of-scope symbol, type T. tree.symbol.ownerChain: value x
+  // [check: patmat] The symbol, tpe or info of tree `(x) : Array[T]` refers to a out-of-scope symbol, type T. tree.symbol.ownerChain: value x
+
+  def g[T](xs: Array[T]): Array[T] = {
+    val x1: Array[T] = xs
+    def case4() = matchEnd3(x1)
+    def matchEnd3(x: Array[T]) = x
+    case4()
+  }
+}
diff --git a/test/pending/pos/treecheckers/c2.scala b/test/pending/pos/treecheckers/c2.scala
new file mode 100644
index 0000000000..c893a5c922
--- /dev/null
+++ b/test/pending/pos/treecheckers/c2.scala
@@ -0,0 +1 @@
+class Test2(val valueVal: Int) extends AnyVal
diff --git a/test/pending/pos/treecheckers/c3.scala b/test/pending/pos/treecheckers/c3.scala
new file mode 100644
index 0000000000..e480bbfb08
--- /dev/null
+++ b/test/pending/pos/treecheckers/c3.scala
@@ -0,0 +1,8 @@
+import scala.collection.mutable.ArrayOps
+
+object Test3 {
+  implicit def genericArrayOps[T](xs: Array[T]): ArrayOps[T] = (xs match {
+    case x: Array[AnyRef]  => refArrayOps[AnyRef](x)
+    case x: Array[Boolean] => booleanArrayOps(x)
+  }).asInstanceOf[ArrayOps[T]]
+}
diff --git a/test/pending/pos/treecheckers/c4.scala b/test/pending/pos/treecheckers/c4.scala
new file mode 100644
index 0000000000..2328131770
--- /dev/null
+++ b/test/pending/pos/treecheckers/c4.scala
@@ -0,0 +1,9 @@
+sealed trait Message[+A]
+class Script[A] extends Message[A] {
+  def iterator: Iterator[Message[A]] = ???
+}
+
+trait Test4[A] {
+  def f(cmd: Message[A]): Iterator[A] = cmd match { case s: Script[t] => s.iterator flatMap f }
+  def g(cmd: Message[A]) = cmd match { case s: Script[t] => s }
+}
diff --git a/test/pending/pos/treecheckers/c5.scala b/test/pending/pos/treecheckers/c5.scala
new file mode 100644
index 0000000000..43cbb65d74
--- /dev/null
+++ b/test/pending/pos/treecheckers/c5.scala
@@ -0,0 +1,3 @@
+trait Factory[CC[X] <: Traversable[X]]
+
+object Test5 extends Factory[Traversable]
diff --git a/test/pending/pos/treecheckers/c6.scala b/test/pending/pos/treecheckers/c6.scala
new file mode 100644
index 0000000000..8283655f3a
--- /dev/null
+++ b/test/pending/pos/treecheckers/c6.scala
@@ -0,0 +1,4 @@
+object Test6 {
+  import scala.reflect.ClassTag
+  def f[T: ClassTag] = implicitly[ClassTag[T]].runtimeClass match { case x => x }
+}