issue: List & Choice Searching

This addresses issues 3703, 3493, 2625, and others where searching for
List or Choice values in a Custom Field will yield no results. This was
due to us using `FIND_IN_SET()` and `IN()` to search, which will not work
with the way the values are stored in the database. This updates the
search methods to use `REGEXP()` to search for the IDs of the List and
Choice values which will give the correct results whether it's multiple
choice or not.

include/class.dynamic_forms.php

@@ -1809,11 +1809,12 @@ class SelectionField extends FormField {
 
     function getSearchQ($method, $value, $name=false) {
         $name = $name ?: $this->get('name');
+        $val = '"?'.implode('("|,|$)|"?', array_keys($value)).'("|,|$)';
         switch ($method) {
         case '!includes':
-            return Q::not(array("{$name}__intersect" => array_keys($value)));
+            return Q::not(array("{$name}__regex" => $val));
         case 'includes':
-            return new Q(array("{$name}__intersect" => array_keys($value)));
+            return new Q(array("{$name}__regex" => $val));
         default:
             return parent::getSearchQ($method, $value, $name);
         }

include/class.forms.php

@@ -1740,11 +1740,12 @@ class ChoiceField extends FormField {
 
     function getSearchQ($method, $value, $name=false) {
         $name = $name ?: $this->get('name');
+        $val = '"?'.implode('("|,|$)|"?', array_keys($value)).'("|,|$)';
         switch ($method) {
         case '!includes':
-            return Q::not(array("{$name}__in" => array_keys($value)));
+            return Q::not(array("{$name}__regex" => $val));
         case 'includes':
-            return new Q(array("{$name}__in" => array_keys($value)));
+            return new Q(array("{$name}__regex" => $val));
         default:
             return parent::getSearchQ($method, $value, $name);
         }