[sane-devel] USB device hotplug detection

[Stef]

     Hello,

     I have added a new test to frontend/tstbackend . When enabled, the 
tstfrontend program loops calling sane_get_devices() function and  print 
detected devices each second, until a given time elapsed. This way you 
can plug/unplug/replug scanners and see if they are correctly reported. 
For instance:
./tstbackend -l0 -r1 -dgt68xx -g35
loops 35 seconds getting devices from gt68xx  backend.

     I have used it to check and fix device detection of the gt68xx. 
This backend, like quite a number of USB backends built its device list 
only in sane_init(), which was wrong, it must be done each time 
sane_get_devices() is called. Failure to do so prevent the backend from 
correctly handling hotplug/unplug of scanners.

     The gt68xx is now fixed regarding this issue.

Regards,
     Stef