ext2_unlink() seems to return EPERM if one attempts to unlink() a
directory.
This seems a bit wrong, would not EISDIR be a better value? I know
that root can sometimes unlink() directories, but even so I think
EISDIR is better for non-root users.
POSIX.1 mandates that the error be EPERM if "the implementation
prohibits using unlink() on directories".
- Ted