Add forgotten test for function specialization

Author: liufengyun

tests/run/multi-apply.scala

@@ -0,0 +1,11 @@
+class MultiApply extends (Int => Int) with ((Int, Int) => Int) {
+  def apply(x: Int): Int = x + x
+  def apply(x: Int, y: Int): Int = x * y
+}
+
+@main
+def Test = {
+  val fun = new MultiApply
+  assert(fun(2) == 4)
+  assert(fun(2, 3) == 6)
+}