- if it's a path to an unmounted file-system listed in /etc/fstab, use
that instead of assuming the user wanted a subtree dump of the parent
directory. this restores the behaviour of dump before the subtree
dumping code went in.
- if it's a path to a mounted file-system which is not in /etc/fstab,
use the info from getmntinfo(3). previously, dump would choke.
* implement error checked malloc(), calloc(), strdup(), and use
appropriately (some of the calloc()s weren't being checked)
* use 'file-system' instead of 'filesystem' in the man page