templatekw: avoid slow creation of changectx objects in showgraphnode() This mitigates the minor perf regression introduced by the previous patch. % hg log -G -R mozilla-central -l10000 --time > /dev/null (original) real 2.200 secs (previous) real 2.590 secs (this) real 2.280 secs

graphlog: extract "graphnode" template keyword that represents node symbol This provides a default node symbol. Tests will be added later. "showparents" variable is renamed to "wpnodes" to avoid confusion with the existing showparents() function.