Have MultibyteStringScanner delegate to StringScanner on Rubinius.
Have MultibyteStringScanner delegate to StringScanner on Rubinius.

Closes #623

askl56/sass,JuanitoFatas/sass,Ahnita/sass,OrenBochman/sass,zaru/sass,MetaAshley/sass,HugoRLopes/sass,Andrey-Pavlov/sass,danielfein/sass,StephanieMak/sass,HugoRLopes/sass,dylannnn/sass,Iamronan/sass,dylannnn/sass,ridixcr/sass,nicklima/sass,Anshdesire/sass,DanteKaris/sass,rammy7219/sass,xzyfer/sass,jaroot32/sass,schneems/sass,nickg33/sass,stewx/sass,modulexcite/sass,lmetla/sass,xzyfer/sass,srinivashappy/sass,askl56/sass,srawlins/sass,srinivashappy/sass,zaru/sass,oss-practice/sass,tangposmarvin/sass,nicklima/sass,baiyanghese/sass,Galactix/sass,lmetla/sass,Anshdesire/sass,ridixcr/sass,Nzaga/sass,Iamronan/sass,OrenBochman/sass,saper/sass,Industrys/sass,amitsuroliya/sass,Ahnita/sass,Andrey-Pavlov/sass,liquidmetal/sass,cmpereirasi/sass,liquidmetal/sass,jaroot32/sass,chriseppstein/sass,modulexcite/sass,DanteKaris/sass,MetaAshley/sass,schneems/sass,amitsuroliya/sass,stewx/sass,saper/sass,briangonzalez/sass,JuanitoFatas/sass,tangposmarvin/sass,srawlins/sass,antonifs/sass,danielfein/sass,cmpereirasi/sass,hcatlin/sass,antonifs/sass,Galactix/sass,PMArtz92/sass,StephanieMak/sass,Industrys/sass,rammy7219/sass,Nzaga/sass,nickg33/sass,PMArtz92/sass,hcatlin/sass