copy: to find copy source, walk parent of revision we're marking copies in
As shown in the previous patch, hg cp --after --at-rev . src dst
fails if src is not in .. It seems obvious that you should always
walk the *parent* of the revision you're marking copies in, but that's
not how it was done for the working copy, and I didn't think to change
it when marking copies in a non-working-copy commit.
This patch fixes that by walking the parent commit instead, but only
if we're marking copies for a non-working-copy commit. We need to
leave the working-copy code unchanged because it depends on the weird
behavior of workingctx.walk(). With these changes, there's very
little overlap between the working-copy version and the
non-working-copy version of walkpats(), but I've refrained from
cleaning that up on the stable branch.
Differential Revision: https://phab.mercurial-scm.org/D8494