Unify module / segment / file drag-drop functionality

[GoogleCodeExporter]

Currently, dropping the text "module:module.spec" or
"segment:segment_name.dvn" onto the canvas will instantiate the relevant
module or segment.

Dropping filenames on the canvas does something reasonable: dvn files are
loaded as networks, vti files as datasets, etc.

This should be unified, so that dragging a module from the module listbox
drags the actual .py filename and not the text.  One could then drop a
module on the canvas to instantiate, or e.g. on an editor to open the file.
 One could also easily copy module sources elsewhere.  The same logic
currently handling filename drops would also handle module drops.

I would REALLY like to integrate this before 8.5, but that's technically
not allowed, as I am too close to releasing.

Original issue reported on code.google.com by cpbotha on 17 Jun 2008 at 9:40

[GoogleCodeExporter]

This is related to issue 66.

Original comment by cpbotha on 17 Jun 2008 at 9:41