Fix of t1123 - Unit discarding

Need to do unit discarding also in selection prototypes.

Author: odersky

src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -79,7 +79,9 @@ object ProtoTypes {
     override def isMatchedBy(tp1: Type)(implicit ctx: Context) = {
       name == nme.WILDCARD || {
         val mbr = tp1.member(name)
-        def qualifies(m: SingleDenotation) = compat.normalizedCompatible(m.info, memberProto)
+        def qualifies(m: SingleDenotation) =
+          memberProto.isRef(defn.UnitClass) ||
+          compat.normalizedCompatible(m.info, memberProto)
         mbr match { // hasAltWith inlined for performance
           case mbr: SingleDenotation => mbr.exists && qualifies(mbr)
           case _ => mbr hasAltWith qualifies

tests/untried/pos/t1123.scala renamed to tests/pos/t1123.scala

@@ -7,5 +7,5 @@ object Test {
     }
     def f = extraListener.h
   }
-  def main(args : Array[String]) : Unit = (new Editor).f
+  def main(args : Array[String]): Unit = (new Editor).f
 }