Allow filtering of what params get serialized

When developing facebook apps, facebook passes lots of fb_* parameters in each request which shouldn't be included in the previous/next/page number links. A quick hack I did to filter these out:

Index: vendor/plugins/will_paginate/lib/will_paginate/view_helpers.rb
===================================================================
--- vendor/plugins/will_paginate/lib/will_paginate/view_helpers.rb      (revision 3718)
+++ vendor/plugins/will_paginate/lib/will_paginate/view_helpers.rb      (revision 3719)
@@ -115,7 +115,7 @@
         @template.content_tag :span, text, :class => span_class
       else
         # page links should preserve GET/POST parameters
-        @template.link_to text, @template.params.merge(param => page != 1 ? page : nil)
+        @template.link_to text, @template.params.reject { |k,v| k[0..2] == 'fb_' }.merge(param => page != 1 ? page : nil)
       end
     end

It'd be nice if we could pass in an ":ignore_params => /^fb_/" type option somewhere.