Experimental cs3200f backend

TODOS:

• where to put the documentation (backend/cs3200f.txt)?
• should the .c includes be removed?
• cancelling a scan does not work correctly (the scan head crashes into the back of the scanner...)
• DPI 75 does not work (the scan head crashes into the back of the scanner...)
• is there a better way to handle the firmware upload?
  • only needing the .DLL file that contains the firmware instead of having to manually extract the correct bytes out of the file
• the last scanlines are not transferred fully, this seems to be a problem with the fifo code
• the warmup is not long enough, most images in the first 10 minutes after turning on the scanner are garbage
• only works with cygwin if pthreads are enabled (by removing the PTHREAD_T_IS_INTEGER) header. this is because the cygwin fork() does not correctly handle the open libusb devices.