Set canmount=off on unmounted overlapping zfs datasets

- Found this wonderful issue after a reboot
Revert /var memory size change - jail files are now on /usr
First part of fix for ticket #2330 , this avoids the traceback
README update to reflect current methods of building FreeNAS
Revert.
Fix _diskcmp to work with geom names

ticket:	#2334
Fix it to instantiate notifier only once

While I'm here do a PEP8 cleanup
srv_enable is a boolean, not an integer
Improve service start/stop notify

This should finally fix cases where SSH service would not start
due to sync issues.
Make sure file exists before stat

ticket:	#2329
ssh reload should call reload and not restart
Rename ftp reverse field accordingly

ticket:	#2323
Hide SNMP trap field for now, it is not being used

ticket:	#2328
Remove comment about TLS certificate

This has already been implemented
FTP field refers only to TLS, not SSL

ticket:	#2324
Description of FTP Banner option is incorrect

ticket:	#2320
Don't build or fetch 64-bit jail files when building for 32-bit.
Add tooltip explaining Always Chroot option for FTP

ticket:	#2321
Fix typo in prefer option for NTP

ticket:	#2332
Allow empty SSL certificate so one is auto-generated

ticket:	#2308