#366935 by drewish - Make the 'Views mode' feature in noderef / ueserref visible even if no usable View exists yet.

#353012 User reference - fix duplicate 'reverse links' on user profile pages when the same user is referenced by several userref fields in a node. Also improves performance by avoiding a full node_load

Fix 'undefined variable' notice when submitting field settings form with 'php code for default value.

Don't assume display_settings[$context] always exists, newly enabled modules may add new contexts that weren't there when the field was last edited.

#336174 (followup) Make sure content_view_field() and content_format() both respect field access rules.

#336174 Move actual field access check in content.module, with content_permission.module providing one permission-based implementation.

#339537 followup - fix upgrade function for db prefixes - make that a new update, to be sure everyone gets it properly.

Diff integration: refactored around a new hook_content_diff_values() to save contrib field modules the
burden of implementing hook_diff. For most field types, the default content_field_content_diff_values()
should be enough, though.

+ abstract a few element validators