Show both elapsed time and estimated remaining time in xz -v.

Show both elapsed time and estimated remaining time in xz -v.

The extra space for showing both has been taken from the
sizes field. If the sizes grow big, bigger units than MiB
will be used. It makes it slightly difficult to see that
progress is still happening with huge files, but it should
be OK in practice.

Thanks to Trent W. Buck for <http://bugs.debian.org/574583>
and Jonathan Nieder for suggestions how to fix it.