libusb1_common, ftdi: clarify libusb_open error message

libusb1_common, ftdi: clarify libusb_open error message

Print a user-friendly message when libusb_open() fails, e.g.
Error: libusb_open() failed with LIBUSB_ERROR_ACCESS
when there's a permissions problem.

Also output a configure warning if libusb older than 1.0.9 is detected.

Change-Id: I800f71f06672fe06c0a98a4e469f853b5021bcfe
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1430
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>