Fix #4016: Translated tags failing to find some tags.

* Normalize spaces to underscores when saving other names. Preserve case
  since case can be significant.

* Fix WikiPage#other_names_include to search case-insensitively (note:
  this prevents using the index).

* Fix sources to return the raw tags in `#tags` and the normalized tags
  in `#normalized_tags`. The normalized tags are the tags that will be
  matched against other names.

test/unit/sources/art_station_test.rb

@@ -56,7 +56,8 @@ module Sources
       end
 
       should "get the tags" do
-        assert_equal(%w[gantz reika], @site.tags.map(&:first))
+        assert_equal(%w[gantz Reika], @site.tags.map(&:first))
+        assert_equal(%w[gantz reika], @site.normalized_tags)
       end
 
       should "get the artist commentary" do
@@ -74,6 +75,11 @@ module Sources
         url = "https://cdna.artstation.com/p/assets/images/images/000/144/922/large/cassio-yoshiyaki-cody2backup2-yoshiyaki.jpg?1406314198"
         assert_equal(url, @site.image_url)
       end
+
+      should "get the tags" do
+        assert_equal(["Street Fighter", "Cody", "SF"].sort, @site.tags.map(&:first).sort)
+        assert_equal(["street_fighter", "cody", "sf"].sort, @site.normalized_tags.sort)
+      end
     end
 
     context "The source site for a http://cdna.artstation.com/p/assets/... url" do