Return 0 if:

1. "-u N" specified, no -f, and mdN found,
2. no -u, "-f /pathname" specified, and mdN associated with /pathname found,
3. "-u N" specified, "-f /pathname" specified, and both of them found,
4. "-l" specified and no -f,
5. "-l" specified, "-f /pathname" specified, and /pathname found.

otherwise return -1.

Spotted by: Julian H. Stacey