scmutil: make shortest() respect disambiguation revset The previous patch would let you use a shorter prefix if the prefix is unique within a configured revset. However, that's not very useful if there's no simple way of knowing what that shorter prefix is. This patch adapts the shortest() template function to use the shorter prefixes for nodes in the configured revset. This is currently extremely slow, because it calculates the revset for each call to shortest(). To make this faster, the next patch will start caching the revset instance. Ideally we'd cache a prefix tree instance instead. Differential Revision: https://phab.mercurial-scm.org/D4038