fetch|clone|--mirror: shorten paths for progress output

fetch|clone|--mirror: shorten paths for progress output

The full pathname for "curl -o ..." was too noisy and confusing.
Reduce confusion by adding the ".tmp" suffix and relying on
"-C".  We'll also avoid displaying "-C" in run_reap() and
rely on "--git-dir=" with "git fetch" to display progress for
users.