- do not read profiles
- tcsh output added to 'export_env()'
- supress errors from 'typeset' in 'save_env()'
- use 'export_env()' to instead of 'echo'
- add global declaration of PMODULES_DEFAULT_GROUPS
  and PMODULES_DEFAULT_RELEASES to 'pmodules_init()'
- add 'tcsh' as supported shell