revlog: fix revlogio.packentry corner case We want to store version information about the revlog in the first entry of its index. The code in packentry was using some heuristics to detect whether this was the first entry, but these heuristics could fail in some cases (e.g. rev 0 was empty; rev 1 descends directly from the nullid and is stored as a delta). We now give the revision number to packentry to avoid heuristics.

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