SI-6614 Test case for fixed ArrayStack misconduct.

Not sure when it was fixed, but in 2.9.2 things were
messed up:

    scala> (for (i <- 0 to 10) yield { val in = ArrayStack.tabulate(i)(_.toString); (in, (in filter (_ => true)) == in) }).mkString("\n")
    res14: String =
    (ArrayStack(),true)
    (ArrayStack(0),true)
    (ArrayStack(0, 1),true)
    (ArrayStack(1, 2, null),false)
    (ArrayStack(0, 1, 2, 3),true)
    (ArrayStack(3, 4, null, null, null),false)
    (ArrayStack(2, 3, 4, 5, null, null),false)
    (ArrayStack(1, 2, 3, 4, 5, 6, null),false)
    (ArrayStack(0, 1, 2, 3, 4, 5, 6, 7),true)
    (ArrayStack(7, 8, null, null, null, null, null, null, null),false)
    (ArrayStack(6, 7, 8, 9, null, null, null, null, null, null),false)

Author: retronym

test/files/run/t6614.check

@@ -0,0 +1,11 @@
+(ArrayStack(),true)
+(ArrayStack(0),true)
+(ArrayStack(0, 1),true)
+(ArrayStack(0, 1, 2),true)
+(ArrayStack(0, 1, 2, 3),true)
+(ArrayStack(0, 1, 2, 3, 4),true)
+(ArrayStack(0, 1, 2, 3, 4, 5),true)
+(ArrayStack(0, 1, 2, 3, 4, 5, 6),true)
+(ArrayStack(0, 1, 2, 3, 4, 5, 6, 7),true)
+(ArrayStack(0, 1, 2, 3, 4, 5, 6, 7, 8),true)
+(ArrayStack(0, 1, 2, 3, 4, 5, 6, 7, 8, 9),true)

test/files/run/t6614.scala

@@ -0,0 +1,8 @@
+object Test extends App {
+	import scala.collection.mutable.ArrayStack
+
+	println((for (i <- 0 to 10) yield {
+		val in = ArrayStack.tabulate(i)(_.toString)
+		(in, (in filter (_ => true)) == in)
+	}).mkString("\n"))
+}