Fix debug output to make it more stable

Avoid printing addresses and reduce junk.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -336,7 +336,7 @@ class Namer { typer: Typer =>
     */
   def enterSymbol(sym: Symbol)(implicit ctx: Context) = {
     if (sym.exists) {
-      typr.println(s"entered: $sym in ${ctx.owner} and ${ctx.effectiveScope}")
+      typr.println(s"entered: $sym in ${ctx.owner}")
       ctx.enter(sym)
     }
     sym

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

@@ -83,6 +83,7 @@ object ProtoTypes {
     def isMatchedBy(tp1: Type)(implicit ctx: Context) = true
     def map(tm: TypeMap)(implicit ctx: Context): ProtoType = this
     def fold[T](x: T, ta: TypeAccumulator[T])(implicit ctx: Context): T = x
+    override def toString = getClass.toString
   }
 
   /** A class marking ignored prototypes that can be revealed by `deepenProto` */