opendous: fix build with libusb-1
opendous: prepend length to commands

All commands sent to the opendous-jtag device need to be prefixed with a
16 bit LE length field.

 #include <stdlib.h> for free()
testing: increase buffer size to avoid overflows

Maybe there's a way to slow down the SVF player?
For now, this does it for my test files.