Fixed gis compiler.get_default_columns()
Fixed some issues in composite fields

 - Made RelatedField VirtualField subclass
 - Allowed update() of composite fields and ForeignKeys, this was
   done by adding resolve_concrete_values() method to Field.
 - By the above, fixed delete SET=None issue
 - Some minor code cleanup (mainly cleaning what VirtualField does,
   and removal of duplicate methods from RelatedField
 - SQLite3 foreign key introspection fix
 - Made subqueries multicolumn friendly by using Query.add_filter()
   instead of manually building the filter conditions
Fixed m2m add, remove, set and clear operations
Added tests for update(combofk=val)
More m2m composite support
Composite M2M value stays selected in forms
Replaced resolve_basic_fields() with concrete_fields cached_property
Removed get_enclosed_field()
Query.values_list() yields tuples for composite fields
Added tests for composite fk attname
Cleaned up related field tuple/nontuple value handling
Merge pull request #3 from akaariai/soc2013/composite-fields

Fixed gis compiler.get_default_columns()
Fixed some issues in composite fields
Fixed m2m add, remove, set and clear operations
Added tests for update(combofk=val)
More m2m composite support
Composite M2M value stays selected in forms
Replaced resolve_basic_fields() with concrete_fields cached_property
Removed get_enclosed_field()
Query.values_list() yields tuples for composite fields
Added tests for composite fk attname
Cleaned up related field tuple/nontuple value handling