[gxvalid] Fix a naming convention conflicting with ftvalid. See previous changeset for otvalid. * src/gxvalid/{gxvcommn.h, gxvmort.h, gxvmorx.h}: Replace `valid' by `gxvalid'. * src/gxvalid/{gxvbsln.c, gxvcommn.c, gxvfeat.c, gxvjust.c, gxvkern.c, gxvlcar.c, gxvmort.c, gxvmort0.c, gxvmort1.c, gxvmort2.c, gxvmort4.c, gxvmort5.c, gxvmorx.c, gxvmorx0.c, gxvmorx1.c, gxvmorx2.c, gxvmorx4.c, gxvmorx5.c, gxvopbd.c, gxvprop.c, gxvtrak.c}: Replace `valid' by `gxvalid' if it is typed as GXV_Validator.