20120809

• New module lino.utils.quantities and new implementation for dd.QuantityField.

  No longer a subclass of DecimalField whose value is a decimals.Decimal, but a CharField whose values are instances of Quantity.

• Bug fixed: NameError “global name ‘IntegrityError’ is not defined”, /lino/ui/extjs3/views.py in form2obj_and_save, line 279