Add missing import of datetime

(transplanted from e0c4f083cd6f7209f24ddacdd67c2ba95bfce550)

tryton/gui/window/form.py

@@ -22,6 +22,7 @@ import pango
 from tryton.translate import date_format
 from tryton.common import DT_FORMAT, DHM_FORMAT, HM_FORMAT
 import mx.DateTime
+import datetime as DT
 
 _ = gettext.gettext