Clarify/clean up code, make fewer assumptions about types:

Clarify/clean up code, make fewer assumptions about types:
- Store pids/gids/uids/devs in a union instead of casting to a long;
- Don't use the nonspecific LT_GENERIC list type;
- Add a more specific LT_PPID list type for parent pids;
- Use NODEV to indicate the lack of a specified device;
- Make the makelist() function more straightforward:
  - use only one switch statement instead of two cascading ones;
  - introduce a helper function parse_pid() to parse pids;
- No functional changes.