Add release parameter to DeviceAttribute::insert

This is a continuation of the problems, discovered in #1057 (closed)

I found, that in PyTango we also can end up in the buggy situation, when we do DeviceAttribute::insert for DevEncoded attribute. At the moment we insert reference to Python`s data array, but we do not notify Python's GC, that somebody uses this object. So it can destroy object before data is taken. Somehow this works, but I cannot understand why. To do it reliably we should copy data and then ask CORBA to clean up.

As far, as I understand, to do it we have to have a control for release parameter, which now is missing.

Is it possible to add it in the same way, as it done for set_value ?