fix calibration file name collision

- handle the case where there are several identical scanners plugged in,
  and avoid sharing the same calibration file
rename MF4550d to MF4500 Series
changelog for recent work
epson2: fixed detection of multiple network-enabled scanners
epson2: improve debug output
epson2: do not reset after each page
epson2: updated usb ids
epson2: fixed ADF detection
epson2: fixed timeout and scanner crash on WP-4540 series (and others)
Canon Pixma MG3200 is working
rename WLAN to WiFi
MX520 supports 14" legal paper size in ADF mode
MX520 has button support
clamp minimum image size to 16 px x 16 px
Canon Pixma MX520 Series is working
changelog for recent work
epson2: fixed another timeout/crash
canon_dr backend v43

- initial DR-M140 support
- add extra_status config and code
- split status code into do_usb_status
- fix copy_line margin offset
- add new color interlacing modes and code
- comment out ssm2
- add timestamp to do_usb_cmd
canon_dr backend v44

- buffermode support for machines with ssm2 command
- DR-M140 needs always_op=0
canon_dr backend v45

- dropout support for machines with ssm2 command
- doublefeed support for machines with ssm2 command