Drillbit support for new protocol revision, miniplane connected boards

Hi Luke,

We have a new Drillbit firmware revision in beta release that supports miniplane support (joining multiple boards into a single unit), some details at http://drillbitsystem.com/forum/index.php?topic=307.0

It also brings a new configuration packet format, which is less ASIC-specific (designed to accommodate our forthcoming Avalon-based miners.) Where we previously had fields for "int clock level" and "ext clock freq", we just have a single frequency field now. For Bitfury "internal" clock levels, there's some new logic in the firmware. Frequencies less than 64 are assumed to be clock levels and set directly. Values >=64 are divided by 5 to convert frequency to level, approximately. I've left the Bfgminer settings alone though, the change is fully "behind the scenes" and settings are defined the same as before.

Commit 4acf6 has a bit more detail about that small tweak in the commit message.

Thanks very much for all your hard work with bfgminer. It's really slick. :)

Please let me know if there's anything you'd like me to change.

Angus