Fixed target difficulty sent to Zeus

-Correct work target difficulty is now sent to Zeus
-HW error count is now displayed correctly
-Performance should improve on slower hosts(rasp-pie)
Fixed issue if pool requests diff < chip count

Fixed an issue where shares would be discarded if the pool is asking
for a work difficulty less than the chip count (rare)

Thanks @kramble
Merge pull request #3 from jstefanop/bfgminer

Fixed target difficulty sent to Zeus