Fix a typo in a MPSSE command in ftdi.h

There is a typo in ftdi.h for the CLK_BYTES_OR_LOW define. It should be
0x9d and not 0x0d.
Added LibFTDI1ConfigVersion to allow version detection
Fixed variable shadowing
No more freshmeat / freecode :(
Make build of the unit tests configurable
Added functions for open using USB file descriptor

Android USB api provides file descriptor. This can
be utilised to make a libusb device. Libusb has been
adequately modified to utilise fd. Added functions which
to use corresponding libusb functions.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Added usb_open_dev_fd for opening on android

Open using provided file descriptor. This function was
earlier left out.
One crucial point is not to close the USB device
( which is done normally by libftdi ).
Nor try to open it again. It is already open.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>