The issue is that sofia siptrace output doesn't end each line with a
newline.  Instead it sends a separate newline afterward, which comes
in as a separate event body.  With the new EL_REFRESH code in effect
the line is being cleared after the siptrace output has been written
but before that next newline comes in.

With our own refresh code this doesn't happen because of slight
differences in where the stdio buffers get flushed compared to where
the output of clear_line() ends up.

This is a bit of a clumsy workaround.  But we'll fix it first, then
refactor.