Errors in in graph calculations

This is the version for 2.1 branch corresponding to https://github.com/pfsense/pfsense/commit/f9983a874d6acf5fcf08a08606a6d19624af4438
XHTML Compliance

Firewall - NAT - Port Forward - Edit
Fix #3486, delete /var/crash content when click 'No'
Merge pull request #980 from N0YB/RELENG_2_1

XHTML Compliance
Merge pull request #979 from phil-davis/RELENG_2_1

Errors in graph calculations
XHTML Compliance

Firewall - NAT - Port Forward - 1 to 1 - Edit
Merge pull request #981 from N0YB/RELENG_2_1

XHTML Compliance
Fix #3492, make sure filesystem is read-write
XHTML Compliance

Firewall - NAT - Outbound - Edit
Return GWG IP protocol (version) when no gateway IP - 2.1 branch
Use return_gateway_groups_array() to build correct GWG list

Version for 2.1 branch
Tidy "gateway name - IP" in dropdown list

for 2.1 branch
Ticket #3484 Note that for now prefixlen is useless in ipv6 tunnels. IPv4 accepts them
Merge pull request #983 from N0YB/RELENG_2_1

XHTML Compliance
Fixes #3484. Provide a dynamic gateway for gif v6 tunnels so it can be used on firewall rules etc. The guide for setting up this tunnels on docs need to change to leave the gif interface as none type. People upgrading need to fix this themselves with a not on release notes. This can be fixed if the kernel condition is relaxed to allow setting the prefixlen on the tunnel as ipv4
Tidy up GWG dropdown selection tests

Tested this making a new rule, and editing existing IPv4, IPv6 and IPv4+Ipv6 rules, and switching the IP version on an existing rule. Seems to work!
Ticket #3484 Correct the case for GRE tunnels as well since they behave the same. GRE seems to need the prefixlen 128 specified all the time so do it explicitly to be on safe side
Add a file flag to trigger the forced serial or else we may miss it during a firmware update and still end up with an accidentally disabled port.
Add an option to verify peers_identifier when it's ASN.1 distinguished name. It should fix #2904
XHTML Compliance

Firewall - NAT - Npt - Edit