- remove "-pdefault" option: redundant with the use of "packages.conf". - remove file pkg/pkg_default : set the default as a pkg group   ("default_pkg_list") defined in pkg/pkg_groups. - fix for case pkg/pkg_depend is missing (was hanging before). - add option "-pgroups" to specify a different pkg_groups than the default.
- remove "-pdefault" option: redundant with the use of "packages.conf".
- remove file pkg/pkg_default : set the default as a pkg group
  ("default_pkg_list") defined in pkg/pkg_groups.
- fix for case pkg/pkg_depend is missing (was hanging before).
- add option "-pgroups" to specify a different pkg_groups than the default.

altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h