This LogCommand was not in my focus (I wanted to do the commit but found out it's hard to test without a log). Therefore I didn't inspected the APIs very well and concentrated only to support a "Log" without any parameters.
But after I looked at the RevWalk again I see that we can easily offer more of the functionality of RevWalk through this API. I'll add at least add() and not() and add(x,y) to support "Log A..B".
I am wondering whether we need a seperate class for RevisionSpecifications and RangeSpecifications. Otherwise we have to add special methods for specifying ranges in a lot of commands. I'll keep this in mind and implement it when I need it.