Update Preprocessor Ember for Ember 1.0.0 pre 4

I've updated the preprocessor for Ember template so that it will work properly with Ember 1.0.0 pre4

N.B. :  I've updated handelbars javascript file to rc2 only for Ember preprocessor, it may be a good idea to also update the preprocessor for Handlebars with the new version, and merge the handlebars file shared between Ember and Handlebars.