[FIX] orm.read_group: fix issues in read_group_full and rewrite/cleanup
[FIX] orm.read_group: fix issues in read_group_full and rewrite/cleanup

Attempt to make it into a more maintainable/readable
separate method.
splbio/openobject-server,splbio/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,vnc-biz/openerp-server,vnc-biz/openerp-server,gisce/openobject-server,gisce/openobject-server,gisce/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server