Define to_a and to_ary

Fix #9

These method definitions are needed for
interacting with array-casting operations
like Array#flatten and Array().

lib/nest.rb

@@ -42,6 +42,14 @@ def to_s
     @ns
   end
 
+  def to_ary
+    nil
+  end
+
+  def to_a
+    nil
+  end
+
   def call(command, *args)
     @rc.call(command, to_s, *args)
   end

test/nest_test.rb

@@ -77,3 +77,13 @@
     assert "s1" == n1.get
   end
 end
+
+# Operations that call to_a and to_ary
+scope do
+  test "interaction with array-casting operations" do
+    n1 = Nest.new("foo")
+
+    assert_equal [n1], [n1].flatten
+    assert_equal [n1],  Array(n1)
+  end
+end