Patch to custom object: object-specific properties (preliminary)

["Marco Contenti" <m contenti libero it>]

Hello,
here is a very first version of what I described last week. Now only four
types are supported. It seems it's working. Please try using it and tell me
what you think about.

Apply the patch to files in <dia>/object/custom, then try using the modified
resistor shape I'm attaching or try making your own, it's simple, just
insert your custom attributes in the shape like this:
<shape ... >
  ...
  <ext_attributes>
   <attribute name="ID" type="string"/>
   <attribute name="Resistance (ohms)" type="int"/>
   <attribute name="Power dissipation (W)" type="real"/>
   <attribute name="SMD package" type="bool"/>
  </ext_attributes>
  ...
</shape>

Yes, I know, all properties get in the same window with standard ones
(context menu Object/Properties), but I'm trying to make it simple.
Suggestions for improvements are welcome.

Thanks and regards.
Marco

custom.patch

hresistor.shape