#97375 More Panels 2 code cleanup and move non-content module Panels integration to relevant module - fieldgroup, nodereference, and userreference.

#186775 - nodereference : fix 'Invalid argument supplied for foreach()' + buggy display when using 'full node' formatter and the referenced node has been deleted
+ updated CHANGELOG with latest commits

 the first set of matches is repeated for subsequent edits (Views query cache)

#152016 (followup) : prevent infinite recursion when using the new 'full node' : 'teaser' formatters.

 since the upgrade - thanks Karen

resulting in repeated "SELECT v.* FROM view_view v WHERE v.name = '--' " queries.
thanks to moggy for noticing this _and_ pinning this down to noderef field

 alex_b and ray007

 (Views) node selection

 'nid'

 the nid / uid

 by ray007

#112464 - refactor userref and noderef validation steps (plus fix / simplify _userreference_potential_references)

 - patch by quicksketch

#112464 standardize validation in field rather than widget, standardize use of $items rather than $node_field

 in content.module)

- updated some invalid strings for translation
- updated .pot file

+ small code reorg

unifying how single and multiple field stores empty field (store 0) - hopefully the last fix for this noderef series, sorry for the back and forth dance