revset: make head() honor order of subset The ordering of 'x & head()' was broken in 6a1a4c212d50 (revset: improve head revset performance, 2014-03-13). Presumably due to other optimizations since then, undoing that change to fix the order does not slow down the simple case of "hg log -r 'head()'" mentioned in that commit. I see a small slowdown from ~0.16s to about ~0.19s with 'not 0 & head()', but I'd say it's worth it for the correct output.