[Haml] Work around the Rails on_load bug.
[Haml] Work around the Rails on_load bug.

Closes gh-142

JuanitoFatas/sass,amatsuda/haml,liquidmetal/sass,hcatlin/sass,nazar-pc/haml,nicklima/sass,sideci-sample/sideci-sample-haml,nicklima/sass,jaroot32/sass,tangposmarvin/haml,PMArtz92/sass,OrenBochman/sass,haml/haml,DanteKaris/sass,dylannnn/sass,Andrey-Pavlov/sass,StephanieMak/sass,Andrey-Pavlov/sass,amitsuroliya/sass,lmetla/sass,StephanieMak/sass,macressler/haml,PMArtz92/sass,nickg33/sass,Iamronan/sass,haml/haml,tangposmarvin/haml,HugoRLopes/sass,askl56/sass,keithpitty/haml,concord-consortium/haml,liquidmetal/sass,Industrys/sass,schneems/sass,xzyfer/sass,srawlins/sass,Ahnita/sass,stewx/sass,dg1dd1ngs/haml,DanteKaris/sass,tenderlove/sass,tangposmarvin/sass,stanhu/haml,JuanitoFatas/sass,HugoRLopes/sass,srawlins/sass,nazar-pc/haml,cmpereirasi/sass,Nzaga/sass,macressler/haml,chriseppstein/sass,schneems/sass,zaru/sass,saper/sass,keithpitty/haml,antonifs/sass,14113/sass,rammy7219/sass,OrenBochman/sass,Industrys/sass,MetaAshley/sass,cmpereirasi/sass,dylannnn/sass,ridixcr/sass,haml/haml,rammy7219/sass,danielfein/sass,stewx/sass,Galactix/sass,Galactix/sass,jaroot32/sass,stanhu/haml,Nzaga/sass,amitsuroliya/sass,Ahnita/sass,oss-practice/sass,modulexcite/sass,xzyfer/sass,zaru/sass,Iamronan/sass,dg1dd1ngs/haml,srinivashappy/sass,chriseppstein/haml,haml/haml,MetaAshley/sass,antonifs/sass,nickg33/sass,Anshdesire/sass,askl56/sass,danielfein/sass,baiyanghese/sass,uniba/hamldoc_ja,chriseppstein/haml,briangonzalez/sass,modulexcite/sass,srinivashappy/sass,lmetla/sass,hcatlin/sass,saper/sass,tangposmarvin/sass,ridixcr/sass,Anshdesire/sass