(cherry picked from commit d34e288)
Facets methods #camelize and #tabto have been duplicated in String extension. #camelize has been rename to #treetop_camelize so I don't step on Rails's version but also don't have to be at its mercy. The #blank? method is only added on String if it hasn't already been defined. Don't define my own version because this one seems pretty hard to get wrong in the manner Treetop uses it.