Rudimentary support for --one-file-system (-x) option

Handle this by recording st_dev and making sure we don't cross into any
files on a different device.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Add option to turn off extent lookup during csum phase.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Merge branch 'one-file-system'

Conflicts:
	duperemove.c

Fixed minor merge conflict in parse_options().

Signed-off-by: Mark Fasheh <mfasheh@suse.de>