+RTS -S -RTS now sends output to stderr (also -s)

+RTS -S -RTS now sends output to stderr (also -s)
Previously +RTS -Sstderr -RTS was required to send output to stderr,
but this is the most common usage and I got tired of typing "stderr".
The old default behaviour of sending output to <prog>.stat is now gone
(I don't think we use it anywhere).

Temporarily we allowed +RTS -S- -RTS to mean stderr; there were
objections to this, so it is now also gone.