def restriction!(restriction)
      @nbuild[NS_EWS_MESSAGES].Restriction {
        restriction.each_pair do |k,v|
          self.send normalize_type(k), v
        end
      }
    end
def restriction!(restriction)
      @nbuild[NS_EWS_MESSAGES].Restriction {
        restriction.each_pair do |k,v|
          self.send normalize_type(k), v
        end
      }
    end
Build the Restriction element
 @see http://msdn.microsoft.com/en-us/library/aa563791.aspx
 @param [Hash] restriction a well-formatted Hash that can be fed to #build_xml!