Fix thinko and add dire warning

If a mapped property had a '-', it would be called like:

document.setProperty('-price', -20.0)

Also, add a warning about trying to set 'variation_category_list' in a
SimulationMovement with property mapping.

product/ERP5/Document/MappedProperty.py

@@ -100,6 +100,10 @@ class MappedProperty(XMLObject):
   security.declarePublic('setMappedProperty')
   def setMappedProperty(self, document, property, value):
     if property.endswith('_list'):
+      # XXX-Leo: This won't work for 'variation_category_list'
+      # calling document.setPropertyList('variation_category_list', value)
+      # breaks with:
+      # TypeError: A mono valued property must be set with a list of len 1
       property = property[:-5]
       setProperty = document.setPropertyList
     else:
@@ -107,6 +111,6 @@ class MappedProperty(XMLObject):
     mapping_dict = self.getMappingDict(reverse=True)
     mapped_property = mapping_dict.get(property, property)
     if mapped_property.startswith('-'):
-      return setProperty(mapped_property, -1 * value)
+      return setProperty(mapped_property[1:], -1 * value)
     else:
       return setProperty(mapped_property, value)