If a publication is 'In Press' use the 'biblio_date' field to store an "Expected In Press" year

#6513 

We already sort on the biblio_date field and it is not used if an item is "In Press", so we use it as a secondary date value here maintaining biblio's fun "text to year" conversion.
Yes, in prepare_view it has already gone through biblio's load function which takes care if this earlier on.