Fix DateTime microsecond replacement

replace method return a new datetime
(transplanted from 9fa480f96eba384f411b9369347d5913d92bbd15)

trytond/backend/fields.py

@@ -118,8 +118,7 @@ class DateTime(Field):
             hours, minutes, seconds = map(int, timepart.split(":"))
             return datetime.datetime(year, month, day, hours, minutes, seconds)
         assert(isinstance(value, datetime.datetime))
-        value.replace(microsecond=0)
-        return value
+        return value.replace(microsecond=0)
 
 
 class Timestamp(Field):

trytond/tests/test_fields.py

@@ -2114,6 +2114,14 @@ class FieldsTestCase(unittest.TestCase):
             }, CONTEXT)
         self.assert_(datetime8_id)
 
+        datetime9_id = self.datetime.create(cursor, USER, {
+            'datetime': today.replace(microsecond=1),
+            }, CONTEXT)
+        self.assert_(datetime9_id)
+        datetime9 = self.datetime.read(cursor, USER, datetime9_id,
+                ['datetime'], CONTEXT)
+        self.assert_(datetime9['datetime'] == today)
+
         cursor.rollback()
         cursor.close()