So far, the snmp detection would stop working after the first response, because libsnmp
haved like that if we return 1 in the callback. Since we want multiple responses to one
broadcast query, we don't tell libsnmp that the response has answered our query.
As a drawback, libsnmp will send the same query in 1-second-intervals, and each device
will answer again. So, we have to keep a list of all devices already detected.
-) LAN and USB communication
-) SNMP LAN auto-detection (using libsnmp, added configure check!)
-) Based on the epson2 backend, with many structural changes
-) B/W, Gray, Color scanning works in 150/300/600dpi (full-page
color scan only possible with <=300dpi)
-) The timeouts (SNMP, scan data, other data) are configurable in the
magicolor.conf file
-) Keeps list of known scanners in sane_get_devices, does not destroy
existing handles; Also correctly calls sanei_usb_init.