[FIX] orm.read_group: fix merge logic for read_group_full:
[FIX] orm.read_group: fix merge logic for read_group_full:

- Properly merge results with list of values, even with reversed sort
- Pass `read_group_order` to `_group_by_full` implementations to let them
  handle sorting if they want.
gisce/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,splbio/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,vnc-biz/openerp-server,splbio/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server