profiling: allow logging profile to the blackbox
This allows specifying '--config profiling.output=blackbox' which will log the
profile output to the blackbox (if enabled). This is useful for doing profiling
on the server since it allows us to record the command, it's result, any
exceptions, and it's profile, all in one spot. And we get log rotation for
free.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state