Fix conflict between normalize and array_attribute macros.

Fix the `normalize` and `array_attribute` macros conflicting with each
other on the WikiPage model. This meant code like
`wiki_page.other_names = "foo bar"` didn't work. Both macros defined a
`other_names=` method, but one method overrode the other.

The fix is to use anonymous modules and prepend so we can chain method
calls with super.

test/unit/wiki_page_test.rb

@@ -101,6 +101,10 @@ class WikiPageTest < ActiveSupport::TestCase
       should normalize_attribute(:other_names).from(["ＡＢＣ"]).to(["ABC"])
       should normalize_attribute(:other_names).from(["foo", "foo"]).to(["foo"])
       should normalize_attribute(:other_names).from(%w[foo*bar baz baz 加賀（艦これ）]).to(%w[foo*bar baz 加賀(艦これ)])
+
+      should normalize_attribute(:other_names).from("foo foo").to(["foo"])
+      should normalize_attribute(:other_names).from("foo bar").to(["foo", "bar"])
+      should normalize_attribute(:other_names).from("_foo_ Bar").to(["foo", "Bar"])
     end
 
     context "during title validation" do