add: pass options via keyword args
The largefiles extensions needs to be able to pass --large, --normal and
--lfsize to subrepos via cmdutil.add() and hgsubrepo.add(). Rather than add
additional special purpose arguments, stop extracting the existing args from the
**opts passed to commands.add() and just pass them along.
Testing that hghave does not crash when checking features
$ "$TESTDIR/hghave" --test-features 2>/dev/null