revlog: use radix tree also for matching keys shorter than 4 hex digits I don't know what the reason for the 4-digit limit was, and I can't think of any real disadvantages of using the radix tree also when the requested minimum length is short. This speeds up `hg log -T '{shortest(node,1)}\n'` from 2m16s to 4.5s by making that not fall back to pure code. Differential Revision: https://phab.mercurial-scm.org/D3453