def _split_path! p
            i = p.rindex Edoors::PATH_SEP
            if i.nil?
                @room = nil
                @door = p
            else
                @room = p[0..i-1]
                @door = p[i+1..-1]
            end
            @door = nil if @door.empty?
        end
def _split_path! p
            i = p.rindex Edoors::PATH_SEP
            if i.nil?
                @room = nil
                @door = p
            else
                @room = p[0..i-1]
                @door = p[i+1..-1]
            end
            @door = nil if @door.empty?
        end
called by Particle#split_dst! to split the path part of the destination

 @param [String] p path to be splitted