vchoi_fork

Changes to be committed:
	modified:   bittests.c
	modified:   cmpd_dset.c
	modified:   dsets.c
	modified:   dt_arith.c
	modified:   dtypes.c
	modified:   extend.c
	modified:   fillval.c
	modified:   filter_fail.c
	modified:   flush1.c
	modified:   gen_cross.c
	modified:   hyperslab.c
	modified:   istore.c
	modified:   links.c
	modified:   links_env.c
	modified:   objcopy.c
	modified:   plugin.c
	modified:   tcheck_version.c
	modified:   unlink.c
	modified:   unregister.c

Minor fixes to replace numeric exit codes with MACRO declarations. Not all codes found were boolean, and those cases were not changed.