adding arc_summary.py from FreeNAS b6494041cf5a7751621ea9b6f992bbf22258c387
comment out stat sections whose kstats are not currently available
port most of arc_summary to use spl kstats
enable l2arc stats
missing newline
include compressed l2size
Merge branch 'arc_summary_draft_v1' of https://github.com/cburroughs/zfs into arcsummary