Add DIGI_POT_HIGH_Z_VREF define.  When defined, Z VREF may exceed 40 and be as high as 118
Fix MBI bug in TWI.cc whereby the I2C clock speed was incorrectly set to 200 KHz when it should have been 100 KHz.  Code used by the RGB LED interface.  For some odd reason, MBI hard coded the AVR clock speed to 8 MHz when (1) it is 16 MHz and (2) a F_CPU #define exists with the correct clock speed.