pfSense

- also rename $section arg to $section_name in some functions to clarify

- also robustify parsing for <tagname> and bulletproof the handling of
certain errors

allow null to be passed as 2nd arg to parse_config_xml*

in which case entire config is returned

fix 'XML error: no Array object found!' errors

log_error if rrdtool restore calls fail

add -f to 'rrdtool restore' call

Teach mwexec and mwexec_bg how to optionally clear signal masks, and use that when launching ntp or ntpdate.

On its own, ntpd does not sync fast enough at bootup, so bring back the ntpdate sync but improve it so it can't get stuck forever.

Clear process signals before exec() or ntpd misbehaves if called from PHP on i386.

As suggested by wagonza, using SAMEORIGIN for X-Frame-Options is sufficient here, and does allow the traffic graphs to work. Fixes #2419

Use FreeBSD's ntpd instead in the backend