OkJson won't work, raise if it's in use.

Author: defunkt

lib/resque/helpers.rb

@@ -1,5 +1,11 @@
 require 'multi_json'
 
+# OkJson won't work because it doesn't serialize symbols
+# in the same way yajl and json do.
+if MultiJson.engine.to_s == 'MultiJson::Engines::OkJson'
+  raise "Please install the yajl-ruby or json gem"
+end
+
 module Resque
   # Methods used by various classes in Resque.
   module Helpers