curl(1) writes to stderr one byte-at-a-time (presumably for the
progress bar). This ends up being unreadable on my terminal
when parallel processes are trying to write error messages.
So instead, we'll capture the output to a file and run
'tail -f' on it if --verbose is enabled.
Since HTTP 404s from non-existent results are a common response,
we'll ignore them and stay silent, matching behavior of local
searches.