Ref T13541. The passthru future does not have time limit behavior, so if we reach this code we currently fail.

Phabricator never reaches this code normally, but this code is reachable during debugging if you try to foreground a slow fetch to inspect it.

Passthru commands generally only make sense to run interactively, and the caller or control script can enforce their own timeouts (usually by pressing "^C" with their fingers).

Used a debugging script to run ref-by-ref fetches in the foreground.