Symbol substutition must consider ClassInfoType#parents

An upcoming change to uncurry, in which I plan to make substitution of
`lambda params -> apply method params` requires that I first to fix a
problem in symbol substition.

This situation can arise when the body of this definition:

    def owner1(a: A) = {
        class C extends M[a.B]
    }

is transplanted into a new owner that has a different symbol for `a`.

I speculated that value classes might also be prone to the
fact that symbol substitution neglected `ClassInfoType#parents`.

We can test change with Value Classes:  Partial Functions that are
dependent on value class param type used to fail with a spurious
overriding error, now they work correctly.

Author: retronym

src/reflect/scala/reflect/internal/tpe/TypeMaps.scala

@@ -717,6 +717,12 @@ private[internal] trait TypeMaps {
           else appliedType(tcon.typeConstructor, args)
         case SingleType(NoPrefix, sym) =>
           substFor(sym)
+        case ClassInfoType(parents, decls, sym) =>
+          val parents1 = parents mapConserve this
+          // We don't touch decls here; they will be touched when an enclosing TreeSubstitutor
+          // transforms the tree that defines them.
+          if (parents1 eq parents) tp
+          else ClassInfoType(parents1, decls, sym)
         case _ =>
           tp
       }

test/files/run/value-class-partial-func-depmet.scala

@@ -0,0 +1,24 @@
+class C
+class A { class C }
+
+object Test {
+  def main(args: Array[String]) {
+    val a = new A
+
+    new VC("").foo(a)
+  }
+}
+
+class VC(val a: Any) extends AnyVal {
+   def foo(a: A) = {
+     val pf: PartialFunction[a.C, Any] = { case x => x }
+     (pf: PartialFunction[Null, Any]).isDefinedAt(null)
+   }
+}
+
+// 2.11.0-M6
+// test/files/run/value-class-partial-func-depmet.scala:14: error: overriding method applyOrElse in trait PartialFunction of type [A1 <: a.C, B1 >: Any](x: A1, default: A1 => B1)B1;
+//  method applyOrElse has incompatible type
+//      val pf: PartialFunction[a.C, Any] = { case x => x }
+//                                          ^
+// one error found