Revise cmd line parsing

[rhc54]

Enforce following precedence order:

1. system-level default parameter file
2. user-level default parameter file
3. Anything found in the environment
4. "--tune" files. Note that "--amca" goes away and becomes equivalent to "--tune". Okay if it is provided more than once on a cmd line (we will aggregate the list of files, retaining order), but an error if a parameter is referenced in more than one file with a different value
5. "--mca" options. Again, error if the same option appears more than once with a different value. Allowed to override a parameter referenced in a "tune" file
6. "-x" options. Allowed to overwrite options given in a "tune" file, but cannot conflict with an explicit "--mca" option
7. all other options