country::multi_select is limited due to varchar(255)

When new custom data set is created and uses a field with country::multi select type data, the table is set up with type VARCHAR(255).

This limits the number of countries selectable to around 50.

This can be confirmed on the demo site (try adding a custom set with a field of type country > multiselect then adding all countries to the field via editing a contact)

changing the columns 'type' to VARCHAR(1024) fixes the problem.