#975400 follow up by bojanz: Give field::sanitize_value more power and fix some issues with get_value.

#1026014 by dereine and alex_b: Use more always should not ask for the count query to see if we need to show the more link.

#1018160 by zhangtaihao: unpack_translatable could infinitely recurse when options are arrays but not declared as such.

#839236: Fields named "buttons" would disappear from the rearrange UI due to conflict with the buttons on the form.

#869172 by bendiy: Add an "external" parameter to field link rewriting so that external URLs can be formed properly even without a scheme.