Returns a array reference of key/value pairs for the column passed in.
Calls $field->label_column to get the column name to use as the label.
The default is name. The labels are sorted by Perls cmp sort.
If there is an active column then only active are included, with the exception
being if the form (item) has currently selected the inactive item. This allows
existing records that reference inactive items to still have those as valid select
options. The inactive labels are formatted with brackets to indicate in the select
list that they are inactive.
The active column name is determined by calling:
$active_col = $form->can( active_column )
Which allows setting the name of the active column globally if
your tables are consistently named (all lookup tables have the same
column name to indicate they are active), or on a per-field basis.
In addition, if the foreign class is the same as the items class (or the class returned
by item_class) then options pointing to item are excluded. The reason for this is
for a table column that points to the same table (self referenced), such as a parent
column. The assumption is that a record cannot be its own parent.