Fixing binding to getters that use lastSetVal

#261

This fixes an issue where if you have a getter using lastSetVal like:

  place: {
    get: function(lastSet){
      if(lastSet) {
        return lastSet;
      }
    }
  }

and were binding to it in a template like:

    {{#if place}}
      THERE IS A PLACE
    {{/if}}

The template would not be updated when setting place.