CyclicError messages now go to printer

Have a configurable printer to which cyclic error messages are sent.

Author: odersky

src/dotty/tools/dotc/config/Printers.scala

@@ -27,4 +27,5 @@ object Printers {
   val incremental = noPrinter
   val config = noPrinter
   val transforms = noPrinter
+  val cyclicErrors = noPrinter
 }

src/dotty/tools/dotc/core/Types.scala

@@ -2864,7 +2864,11 @@ object Types {
   object CyclicReference {
     def apply(denot: SymDenotation)(implicit ctx: Context): CyclicReference = {
       val ex = new CyclicReference(denot)
-      if (!(ctx.mode is typer.Mode.CheckCyclic)) ex.printStackTrace()
+      if (!(ctx.mode is typer.Mode.CheckCyclic)) {
+        cyclicErrors.println(ex.getMessage)
+        for (elem <- ex.getStackTrace take 40)
+          cyclicErrors.println(elem.toString)
+      }
       ex
     }
   }