library: normalize the <pids> fill/selection interface
After wrestling with the conversion of both top and ps
the differences between reap (all) & fill (select) has
become increasingly inconvenient. So this patch simply
normalizes that API making returned results identical.
The former procps_pids_stacks_fill identifier will now
be known as procps_pids_select which serves as logical
counterpart to the existing procps_pids_reap function.
Signed-off-by: Jim Warner <james.warner@comcast.net>