[7.0][ocb-only] Report "report.stock.lines.date" not supported by postgresql < 9.1

Addons revno 10181

SQL view created for report _name = 'report.stock.lines.date' is not supported by Postgresql 9.0 or older.

That's what I've found out:
* Revision 10142 added a new field for this SQL view "active" (ref: http://bazaar.launchpad.net/~ocb/ocb-addons/7.0/revision/10142#stock/report/report_stock.py)
* Postgresql version 9.0 and older does not support referring to a column which is not in group by clause if this clause is present (ref: http://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-GROUPBY)

Please find patch attached.

Cheers
Andrius