[PATCH 0 of 2] Let progress act as a silencer

[timeless]

mpm didn't like the hackery I was using for convert.

It turns out that what we really want is just to treat the progress extension
as a request for "quiet". If the user actually wants noisy, then this doesn't
apply.

Unfortunately the progress extension also generates output which upsets
run-tests.py - as it often leaves an incomplete line when it's "done".

With this, the tests pass and the result is pleasing to my eyes.