Fix problem with TermRef equality.

Equality was not symmetric between TermRefs and TermrefWithSignatures.

Author: odersky

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

@@ -1339,7 +1339,8 @@ object Types {
       case that: NamedType =>
         this.name == that.name &&
         this.prefix == that.prefix &&
-        !that.isInstanceOf[TermRefWithSignature]
+        !that.isInstanceOf[TermRefWithSignature] &&
+        !that.isInstanceOf[WithFixedSym]
       case _ =>
         false
     }