#17 objects of Templates without DConstructors won't show up

[Reuben Grinberg]

The function getExtraConstructorCode gets inserted into all
DConstructors at the end. However, if there are no DConstructors,
this code will never get run.

Since DObjectTemplate relies upon this code ( a DynamicObject
registering itself with the template when it is constructed) in order to
see what objects are made from it, objects without a DConstructor
won't show up in the DObjectManager list.