* backend/epjitsu.[ch], backend/epjitsu-cmd.h: backend v 13, 14 and 15:
- add working page-height control
- add working brightness, contrast and threshold controls
- add disabled threshold curve and geometry controls
- move initialization code to sane_get_devices, for hotplugging
- support S300 on USB power
- support S300 225x200 and 600x600 scans
- support for automatic paper length detection (parm.lines = -1)
- expose hardware buttons/sensors as options for S300
* doc/descriptions/epjitsu.desc: change S300 status to good