Merge branch 'better-type-reporting-1' of github.com:rssh/dotty into better-type-reporting-1

Author: rssh

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -284,7 +284,7 @@ import transform.SymUtils._
 
     override def explain = 
       val treeStr = inTree.map(x => s"\nTree: ${x.show}").getOrElse("")
-      treeStr + "\n" + err.whyNoMatchStr(found, expected)
+      treeStr + "\n" + super.explain
 
 
   end TypeMismatch