Invalide fullName cache when name changes

Also: use "_$" instead of "~" as filler when taking the full name
of a term member. If the term member is symbolic (e.g. +) the
filler name would be misinterpreted as a symbolic name "~+", so would
be mangled as "$tilde$plus$ instead of "~$plus".

Author: odersky

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -397,7 +397,7 @@ object SymDenotations {
         var encl = owner
         while (!encl.isClass && !encl.isPackageObject) {
           encl = encl.owner
-          filler += "~"
+          filler += "_$"
         }
         var prefix = encl.fullNameSeparated(kind)
         if (kind.separator == "$")
@@ -499,7 +499,7 @@ object SymDenotations {
      *  step for creating Refinement types.
      */
     final def isRefinementClass(implicit ctx: Context): Boolean =
-      name.decode == tpnme.REFINE_CLASS
+      name == tpnme.REFINE_CLASS
 
     /** Is this symbol a package object or its module class? */
     def isPackageObject(implicit ctx: Context): Boolean = {