Fix to printing type parameters.

Printing a type parameter reference `A#T` now only reduces to `T` if
`A` is some `B.this.type`.

Author: odersky

src/dotty/tools/dotc/core/transform/Erasure.scala

@@ -247,7 +247,7 @@ class Erasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcard
       sigName(tp.optBounds)
     case _ =>
       val erased = this(tp)
-      assert(erased ne tp)
+      assert(erased ne tp, tp)
       sigName(erased)
   }
 }

src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -110,9 +110,9 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         }
       case tp: TypeRef =>
         if ((tp.symbol is TypeParam | TypeArgument) && !ctx.phase.erasedTypes) {
-          return tp.info match {
-            case TypeAlias(hi) => toText(hi)
-            case _ => nameString(tp.symbol)
+          tp.info match {
+            case TypeAlias(hi) => return toText(hi)
+            case _ => if (tp.prefix.isInstanceOf[ThisType]) return nameString(tp.symbol)
           }
         }
         else if (tp.symbol.isAnonymousClass)