This breakage seems to have been caused way back in a1eded86,
but I am pretty sure rsync.net support has not been entirely
broken since last April. AFAICS, the generated .ssh/config
has not changed since then -- it has never included a Username setting
line. So, I am puzzled at when this reversion was introduced.
Note that the breakage only affected checkpresent and remove. Upload and
download use the ssh connection caching, which includes a -l username.
