hgweb: use generator to count parity of horizontal stripes for easier reading.
- use web.stripes in all places and consistently
- start with parity0 for lists generated in reverse (e.g. changelog)
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