Silence warnings in lib/haml/filters.rb
Silence warnings in lib/haml/filters.rb

Use attr_writer to avoid method redefined warnings when generated
method is redefined.

Check if @template_class is defined to avoid variable not initialized
warning.

amatsuda/haml,dg1dd1ngs/haml,haml/haml,nazar-pc/haml,keithpitty/haml,dg1dd1ngs/haml,keithpitty/haml,haml/haml,nazar-pc/haml,tangposmarvin/haml,stanhu/haml,sideci-sample/sideci-sample-haml,haml/haml,macressler/haml,tangposmarvin/haml,stanhu/haml,macressler/haml,haml/haml