* fhandler.cc (fhandler_base::fchmod): Do the right thing when changing an "on

* fhandler.cc (fhandler_base::fchmod): Do the right thing when changing an "on
disk" device or fifo.
(fhandler_base::fchown): Ditto for changing ownership.
* fhandler_disk_file.cc (fhandler_base::fstat_helper): Accommodate device files
on ntfs partitions.
* path.cc (path_conv::check): Use isfs function to figure out if a path exists
on a filesystem to make sure that device files are caught.