usbmount fixes

- create mounting points
- fix dependencies
- fix udev rules
- fix fs type detection

[Peter: fix Config.in deps, create usb7, only remove /media/usb?]
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>