dirstate: add __contains__ and make __getitem__ more useful
dirstate.state(f) == '?' -> f not in dirstate
dirstate.state(f) -> dirstate[f]
foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
rev offset length base linkrev nodeid p1 p2
0 0 6 0 0 26d3ca0dfd18 000000000000 000000000000
1 6 7 1 1 d267bddd54f7 26d3ca0dfd18 000000000000