Review Board now sends special headers along with review e-mails

indicating if a review contains a "Ship It!" (in which case it will

contain the X-ReviewBoard-ShipIt header) or if it only contains a

"Ship It!" it (in which case both the X-ReviewBoard-ShipIt and

X-ReviewBoard-ShipIt-Only headers will be sent).
Test cases have been added that cover all possible review scenarios.

Ran unit tests.