Also changed usbdev, usbsn, usbvendor and usbproduct components from
PROGRAMMER structure to be cached string pointers rather than fixed-size
arrays. These will be initialised by pgm_new() with a pointer to nul;
Previously, all libusb-1.0 error strings have been translated
by libusb_to_errno() into an errno-like integer, only in order
to pass that one straight into strerror().
For unhandled libusb-1.0 error codes, ERANGE was returned, which
is just nonsense ("Result too large", bug #848).
Instead, use a single function errstr() now that either can
use strerror() on some well-defined errno-like code, or otherwise
just return a string that mentions the numeric value.
Stefan Rueger
Joerg Wunsch
Marius Greuel