SI-9206 Update REPL welcome message

Everyone knows that a `help` command will result in `more information`.

This commit moves the version string to the second line and adds some
verve to the welcome.

If anyone can't live without the old banner, they are now able to
configure it explicitly, so there is still no blood on our hands.
```
$ scala
Welcome to Scala version 2.11.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_40).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :quit
$ skala
Welcome to Scala!
version 2.11.7-20150623-155244-eab44dd092 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_40).
Type in expressions for evaluation. Or try :help.

scala> :quit
```
REPL tests now lop off the actual length of the welcome header; or, if
necessary, remove the version number from a header embedded in output.

1 files changed, 3 insertions, 4 deletions

diff --git a/test/files/run/repl-trim-stack-trace.scala b/test/files/run/repl-trim-stack-trace.scala
index b8c1668691..d128d4c39a 100644
--- a/test/files/run/repl-trim-stack-trace.scala
+++ b/test/files/run/repl-trim-stack-trace.scala
@@ -4,9 +4,9 @@ import scala.tools.partest.{ SessionTest, Welcoming }
 // SI-7740
 object Test extends SessionTest with Welcoming {
   def session =
-"""Welcome to Scala
-Type in expressions to have them evaluated.
-Type :help for more information.
+"""Welcome to Scala!
+version
+Type in expressions for evaluation. Or try :help.
 
 scala> def f = throw new Exception("Uh-oh")
 f: Nothing
@@ -37,7 +37,6 @@ scala> :quit"""
   // normalize the "elided" lines because the frame count depends on test context
   lazy val elided = """(\s+\.{3} )\d+( elided)""".r
   override def normalize(line: String) = line match {
-    case welcome(w)               => w
     case elided(ellipsis, suffix) => s"$ellipsis???$suffix"
     case s                        => s
   }