checkcopies: handle divergences contained entirely in tca::ctx During a graftlike merge, _checkcopies runs from ctx to tca, possibly passing over the merge base. If there is a rename both before and after the base, then we're actually dealing with divergent renames. If there is no rename on the other side of tca, then the divergence is contained entirely in the range of one _checkcopies invocation, and should be detected "in the loop" without having to rely on the other _checkcopies pass.