[2.2] Changes communication between appender and forcer in batched writes

to only rely on appender ticket and force ticket, w/o even involving last
committed transaction id, which was an unncessary involvement.
Also added tests to absolutely make sure that appender waits for correct
round of force, even in the face of ticket long values wrapping around
Long.MAX_VALUE.
No particular reason. It's just that this duration virtually doesn't matter since appenders unparks the forcer thread anyway. Would you agree?