Fix RefinementType#member

Type members used to always pick the last refined info for a type name.
This is incorrect, as a type might have several refinements for the
same type name, which are not necessarily subsumed by the last one.
We now only pick the last one if it is an alias type (assuming we check
for conflicts elsewhere).

Author: odersky

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

@@ -375,9 +375,10 @@ object Types {
       def goRefined(tp: RefinedType) = {
         val pdenot = go(tp.parent)
         val rinfo = tp.refinedInfo.substThis(tp, pre)
-        if (name.isTypeName) // simplified case that runs more efficiently
-          pdenot.asSingleDenotation.derivedSingleDenotation(pdenot.symbol, rinfo)
-        else
+        if (name.isTypeName) {// simplified case that runs more efficiently
+          val jointInfo = if (rinfo.isAlias) rinfo else pdenot.info & rinfo
+          pdenot.asSingleDenotation.derivedSingleDenotation(pdenot.symbol, jointInfo)
+        } else
           pdenot & (new JointRefDenotation(NoSymbol, rinfo, Period.allInRun(ctx.runId)), pre)
       }
       def goThis(tp: ThisType) = {