Fix #1898: Include alias predicates in non-empty Tags search.

Make searches on the /tags index includes aliases too. Show matching
aliases like this:

   Name: gray*

   ? 75098 grey_hair <- gray_hair
   ? 35345 grey_eyes <- gray_eyes

config/initializers/core_extensions.rb

@@ -31,6 +31,11 @@ module Danbooru
       def falsy?
         self.match?(/\A(false|f|no|n|off|0)\z/i)
       end
+
+      def ilike?(pattern)
+        pattern = Regexp.escape(pattern).gsub(/\\\*/, ".*")
+        match?(/\A#{pattern}\z/i)
+      end
     end
   end
 end