Added i2cLock() -- still untested.
Verifying that i2cLock() does not break anything when not used
disable DMA moved from endDMA to processRx/Reply

Works with existing tests.  i2cLock() still untested...
first working i2cLock() API

don't like the repeated starts...
i2cLock debugged (no repeated starts until next msg begun)

Reworked, improved error handling
Threads stops are awoken with I2CD_STOPPED error on i2c_stop()