compat: add a fixed version of mergecopies for hg<=4.3
In hg<=4.3, copies._fullcopytracing() does not exist and we have to wrap
copies.mergecopies() to fix the AssertionError coming from core.
#require test-repo
$ checkcm() {
> if ! (which check-manifest > /dev/null); then
> echo skipped: missing tool: check-manifest;
> exit 80;
> fi;
> };
$ checkcm
$ cat << EOF >> $HGRCPATH
> [experimental]
> evolution=all
> EOF
Run check manifest:
$ cd $TESTDIR/..
$ check-manifest
lists of files in version control and sdist match