Fix I2C endTransmission(false) with USCI

Fixes Wire.endTransmission(false) for MSP430G2553 (USCI). This will
allow to read from I2C devices with restart condition.
See http://forum.43oh.com/topic/3154-i2c-issues/#entry34292
Arduino compatible millisecond tracking

Updated how Energia tracks milliseconds to make output of millis() and
micros() identical with Arduino. This will fix issues with millis()
roll-over after 11 hours and not using the full 32bit available. The
millisecond timer now rolls over after approx. 50 days and basic
comparison like if(now - start > period) now works safely.

Implementation is mostly a direct port from latest Arduino version of
wiring.c. Compilation size is identical or only a few bytes bigger.
Merge pull request #235 from astuder/i2c-fixes

Fix I2C endTransmission(false) with USCI

Arduino compatible millisecond tracking