Debugger: Make Creator work with a GDB using Python 3.x

Even if current GDB git does not compile in that configuration,
some people seem to be able to get this up and running, leading
to dumper load failures and fallback to the no-more-existing
compiled dumpers.

Change-Id: I08ba6c43105c28b3406fce36049bfdf633e79e31
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: David Schulz <david.schulz@digia.com>