in gravity.m: replaced the 'ggm05g' test with 'mascons'; removed the 'gracec20' test; revised the 'stats' test
in gravity.m: replaced the 'ggm05g' test with 'mascons'; removed the 'gracec20' test; revised the 'stats' test

jgte/orb,jgte/orb,jgte/orb,jgte/orb,jgte/orb