Fix #782: Add regression test

Author: allanrenucci

tests/pos/i782.scala

@@ -0,0 +1,15 @@
+class M
+
+class A extends M
+class B extends M
+
+class Foo[T](x: T) {
+  def foo[S >: T](other: S): Foo[S] = ???
+}
+
+object C {
+  def xy() = {
+    val x: Foo[A] = new Foo(new A)
+    x.foo(new B)
+  }
+}