Fix for Context#withPhase

Author: odersky

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

@@ -280,8 +280,8 @@ object Contexts {
     final def withMode(mode: Mode): Context =
       if (mode != this.mode) fresh.withNewMode(mode) else this
 
-    final def withPhase(phase: PhaseId): Context =
-      if (this.phaseId == phaseId) this else fresh.withNewPhase(phase)
+    final def withPhase(phaseId: PhaseId): Context =
+      if (this.phaseId == phaseId) this else fresh.withNewPhase(phaseId)
     final def withPhase(phase: Phase): Context =
       withPhase(phase.id)