Fix Transaction.start to use keyword argument for context

(transplanted from d2f919d970fb08f0da63127fc7e2f2bfd4919a27)

tests/test_product.py

@@ -41,7 +41,8 @@ class ProductTestCase(unittest.TestCase):
         '''
         Test uom non_zero_rate_factor constraint.
         '''
-        with Transaction().start(DB_NAME, USER, CONTEXT) as transaction:
+        with Transaction().start(DB_NAME, USER,
+                context=CONTEXT) as transaction:
             category_id = self.uom_category.create({'name': 'Test'})
             transaction.cursor.commit()
 
@@ -83,7 +84,8 @@ class ProductTestCase(unittest.TestCase):
         '''
         Test uom check_factor_and_rate constraint.
         '''
-        with Transaction().start(DB_NAME, USER, CONTEXT) as transaction:
+        with Transaction().start(DB_NAME, USER,
+                context=CONTEXT) as transaction:
             category_id = self.uom_category.search([
                 ('name', '=', 'Test'),
                 ], limit=1)[0]
@@ -123,7 +125,7 @@ class ProductTestCase(unittest.TestCase):
             ('centimeter', 'rate'),
             ('Foot', 'factor'),
         ]
-        with Transaction().start(DB_NAME, USER, CONTEXT) as transaction:
+        with Transaction().start(DB_NAME, USER, context=CONTEXT):
             for name, result in tests:
                 uom_id = self.uom.search([
                     ('name', '=', name),
@@ -143,7 +145,7 @@ class ProductTestCase(unittest.TestCase):
             ('Second', 25, 'Hour', 0.0069444444444444441, 0.01),
             ('Millimeter', 3, 'Inch', 0.11811023622047245, 0.12),
         ]
-        with Transaction().start(DB_NAME, USER, CONTEXT) as transaction:
+        with Transaction().start(DB_NAME, USER, context=CONTEXT):
             for from_name, qty, to_name, result, rounded_result in tests:
                 from_uom = self.uom.browse(self.uom.search(
                     [
@@ -176,7 +178,7 @@ class ProductTestCase(unittest.TestCase):
             ('Second', Decimal('25'), 'Hour', Decimal('90000')),
             ('Millimeter', Decimal('3'), 'Inch', Decimal('76.2')),
         ]
-        with Transaction().start(DB_NAME, USER, CONTEXT) as transaction:
+        with Transaction().start(DB_NAME, USER, context=CONTEXT):
             for from_name, price, to_name, result in tests:
                 from_uom = self.uom.browse(self.uom.search(
                     [