Added iPad compatibility via extra board type. Cludgy, perhaps, but work...

Hey

Gave this a whirl. Best way I saw to do this is add a second board to the ARcore which has an inline compiler define (-DIPAD_COMPAT, which is equivalent to #define IPAD_COMPAT). We then test for this in USBcore and switch between two current settings (500mA, or 20mA for iPad compatibility).

Let me know what you think - I tested it and it seems to work.

Stefan