code: function( url ) {
  			var parts = this.path.split('/'),
  				other_parts = url.split('/'),
  				result = '';
  			while ( parts.length > 0 && other_parts.length > 0 && parts[0] == other_parts[0] ) {
  				parts.shift();
  				other_parts.shift();
  			}
  			each(other_parts, function(){ result += '../'; })
  			return result + parts.join('/');
  		}
docs: Returns the relative path between two paths with common folders.
  @codestart
  new steal.File('a/b/c/x/y').toReferenceFromSameDomain('a/b/c/d/e')//-> ../../x/y
  @codeend
  @param {Object} url
  @return {String}