Update to Grace 5.1.23

Changes in 5.1.23

  Bug fixes
* [ES] removed *86 specific optimizations (rep. #2154)
* [ES] renamed RMS per cent error -> relative error (rep. #2192)
* [ES] a workaround for a bug in recent Xorg not releasing grab of popup menus
* [ES] accept -graphtype chart instead of bar. List possible values in the
        help output
* [TK] fix building against png-1.5
* [SM] a grace_np fix
* [ES] IsoLatin5.enc was not included in the distribution

(asau)