templater: use unfiltered changelog to calculate shortest() at constant time
cl._partialmatch() can be pretty slow if hidden revisions are involved. This
patch cancels the slowdown introduced by the previous patch by using an
unfiltered changelog, which means shortest(node) isn't always the shortest.
The result isn't perfect, but seems okay as long as shortest(node) is short
enough to type and can be used as an identifier.
(with hidden revisions)
% hg log -R hg-committed -r0:20000 -T '{node|shortest}\n' --time > /dev/null
(.^^) time: real 1.530 secs (user 1.480+0.000 sys 0.040+0.000)
(.^) time: real 43.080 secs (user 43.060+0.000 sys 0.030+0.000)
(.) time: real 1.680 secs (user 1.650+0.000 sys 0.020+0.000)