SI-7781 REPL stack trunc shows cause

The handy stack trace truncation in REPL doesn't
show cause like a regular trace.

This commit fixes that and also adds the usual
indicator for truncation, viz, "... 33 more".

The example from the ticket produces:

```
scala> rewrapperer
java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: Point of failure
  at .rewrapper(<console>:9)
  at .rewrapperer(<console>:10)
  ... 32 elided
Caused by: java.lang.RuntimeException: java.lang.RuntimeException: Point of failure
  at .wrapper(<console>:8)
  ... 34 more
Caused by: java.lang.RuntimeException: Point of failure
  at .sample(<console>:7)
  ... 35 more
```

Suppressed exceptions on Java 7 are handled reflectively.

```
java.lang.RuntimeException: My problem
  at scala.tools.nsc.util.StackTraceTest.repressed(StackTraceTest.scala:56)
  ... 27 elided
  Suppressed: java.lang.RuntimeException: Point of failure
    at scala.tools.nsc.util.StackTraceTest.sample(StackTraceTest.scala:29)
    at scala.tools.nsc.util.StackTraceTest.repressed(StackTraceTest.scala:54)
    ... 27 more
```

1 files changed, 8 insertions, 0 deletions

diff --git a/test/files/run/repl-trim-stack-trace.scala b/test/files/run/repl-trim-stack-trace.scala
index bbf46f2f19..db42b37fdd 100644
--- a/test/files/run/repl-trim-stack-trace.scala
+++ b/test/files/run/repl-trim-stack-trace.scala
@@ -13,6 +13,7 @@ f: Nothing
 scala> f
 java.lang.Exception: Uh-oh
   at .f(<console>:7)
+  ... 69 elided
 
 scala> def f = throw new Exception("")
 f: Nothing
@@ -20,6 +21,7 @@ f: Nothing
 scala> f
 java.lang.Exception: 
   at .f(<console>:7)
+  ... 69 elided
 
 scala> def f = throw new Exception
 f: Nothing
@@ -27,7 +29,13 @@ f: Nothing
 scala> f
 java.lang.Exception
   at .f(<console>:7)
+  ... 69 elided
 
 scala> """
 
+  // remove the "elided" lines because the frame count is variable
+  lazy val elided = """\s+\.{3} (?:\d+) elided""".r
+  def filtered(lines: Seq[String]) = lines filter { case elided() => false ; case _ => true }
+  override def eval() = filtered(super.eval().toSeq).iterator
+  override def expected = filtered(super.expected).toList
 }