unionrepo: avoid unnecessary node -> rev conversion

bundlerepo: avoid unnecessary node -> rev conversion

revlog: avoid unnecessary node -> rev conversion

check-code: detect r.revision(r.node(rev)) revlog.revision takes either node or rev, but taking a rev is more efficient, because converting rev to node is just a seek and read. That's cheaper than converting node to rev, which may require O(n) walk in revlog index for the first times, and then triggering building the radix tree index. Even with the radix tree built, rev -> node is still faster than node -> rev because the radix tree requires more jumps in memory. So r.revision(r.node(rev)) should be changed to r.revision(rev). This patch adds a check-code rule to detect that.