Fix to asSeenFrom for package object members

Like TypeAssigner, asSeenFrom needs to insert a package object if the
prefix is a package but the class enclosing the type is not.

Author: odersky

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

@@ -22,6 +22,8 @@ trait TypeOps { this: Context =>
           case SuperType(thispre, _) => thispre
           case _ => pre
         }
+      else if ((pre.termSymbol is Package) && !(thiscls is Package))
+        toPrefix(pre.select(nme.PACKAGE), cls, thiscls)
       else
         toPrefix(pre.baseTypeRef(cls).normalizedPrefix, cls.owner, thiscls)
     }

tests/pos/i0239.scala

@@ -0,0 +1,24 @@
+package p {
+  class C[A] {
+    implicit def foo: M[A] = ???
+  }
+
+  object `package` extends C[String]
+
+  object test0 {
+    def compute[A](implicit m: M[A]): A = ???
+    val v = compute
+    val v1: String = v
+  }
+}
+
+trait M[A]
+
+object test1 {
+
+  def compute[A](implicit m: M[A]): A = ???
+
+  import p._
+  val v = compute
+  val v1: String = v
+}