[FIX] res_currency remove warning about float field

bzr revid: al@openerp.com-20120208224031-korqq1crt0u3wpuh

openerp/addons/base/res/res_currency.py

@@ -233,8 +233,7 @@ class res_currency_rate(osv.osv):
 
     _columns = {
         'name': fields.date('Date', required=True, select=True),
-        'rate': fields.float('Rate', digits=(12,6), required=True,
-            help='The rate of the currency to the currency of rate 1'),
+        'rate': fields.float('Rate', digits=(12,6), help='The rate of the currency to the currency of rate 1'),
         'currency_id': fields.many2one('res.currency', 'Currency', readonly=True),
         'currency_rate_type_id': fields.many2one('res.currency.rate.type', 'Currency Rate Type', help="Allow you to define your own currency rate types, like 'Average' or 'Year to Date'. Leave empty if you simply want to use the normal 'spot' rate type"),
     }