Advanced related objects

*Title: Advanced related objects

*Documentation:
Object relations made with datatypes 'ezobjectrelationlist' and
'ezobjectrelation' are now stored in 'ezcontentobject_link' table too.
New field 'contentclassattribute_id' has been added to this table to distinguish
between object relations of different types. The value of this field is an ID
of an attribute that stores information about relations, or zero if this is a
common object relation (default value of the field).

All relations to an object made with datatypes will be removed when you delete
an object. Function eZDataType::removeRelatedObjectItem removes items with
given objectID from the relations list stored in the attribute.
For now it is implemented for 'ezobjectrelationlist' and 'ezobjectrelation'
datatypes.

Documentation on new template fetch functions can be found in this file:

related_objects_fetch_functions.txt


*Upgrade database:
If you are using database created with the previous version of Exponential (3.5 or
 lower), follow these steps:
1. Upgrade database structure using SQL script that you can find in update/database
directory.
2. Run update/common/scripts/updaterelatedobjectslinks.php script to update existing
related objects links.