Both link paths -- --remote and the --server/$GIT_SERVER link-existing
branch -- called `git remote add origin` bare. That fails with "remote
origin already exists" whenever the target is already linked, which is
the normal case for `mkrep .` against an existing checkout and for any
rerun against the same target. The failure took the whole call down with
exit 1.
Route both through a new _mkrep_add_origin helper: add when there is no
origin, accept and report when origin already points at the requested
URL, and refuse when it points elsewhere. A different URL is a different
repo, so repointing stays the caller's explicit decision rather than a
silent rewrite of a checkout mkrep may have been aimed at by mistake.
rootiest