Trying to display external identifiers would make the server crash
because the method in charge of requesting the external id information
would expect an object but it was being given a string and thus not
computing the m2o_value for the record.
This commit fixes this by changing FieldMany2One objects' m2o_value
instatiation to use its _formatValue method to compute it, _formatValue
is then overridden in FieldReference so that it properly handles both
strings and objects to calculate its m2o_value and relation.
Elkasitu
a4e30a1b43