THE GLOBULAR CLUSTER SYSTEMS IN THE COMA ELLIPTICALS. IV: WFPC2 PHOTOMETRY FOR FIVE GIANT ELLIPTICALS **Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555., ****This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.