new behaviour for --rcluster-max and --rcluster-percent

The defaults are now:

--rcluster-max 1000
--rcluster-percent 100

These are pretty sensible, and will run fast on most machines and give
good answers on most datastests.

There is also the option to set
--rcluster-max -1

in which case it is ignored completely, and only --rcluster-percent is
used.