use parameterize to convert the string

this is more efficient, and works on more cases. parameterize was introduced in rails 2.3.2

lib/dehumanize.rb

@@ -1,11 +1,11 @@
 module ActiveSupport::Inflector
-  def dehumanize(the_string)
-    the_string.gsub(' ', '_').downcase
+  def dehumanize(string)
+    string.parameterize.underscore
   end
 end
 
 class String
   def dehumanize
     ActiveSupport::Inflector.dehumanize(self)
   end
-end
+end