Revision 2104

Final step for explicit id/geometry columns: Loading and saving

* Resources/XML/thuban-1.1.dtd: New.  Derived from thuban-1.0.dtd
with the following changes:
(dbshapesource): Two new attributes id_column and geometry_column

* Thuban/Model/save.py (SessionSaver.write): Use the new dtd
(SessionSaver.write_session): Use the new namespace
(SessionSaver.write_data_containers): Write the new dbshapesource
parameters

* Thuban/Model/load.py (SessionLoader.__init__): New namespace for
the new file format version
(SessionLoader.start_dbshapesource): Handle the new db parameters

* test/test_save.py: Update to the new dtd and namespace
(SaveSessionTest.test_save_postgis): Update the NonConnectionStore
mock object to provide a working IDColumn method.

* test/test_load_1_0.py: New.  Copy of the test_load.py before
today's changes but with the round-trip tests removed.

* test/test_load_0_9.py: Update doc-string.

* test/test_load.py: Update all .thuban files to the new dtd and
namespace.
(TestPostGISLayer.file_contents): Add the new dbshapesource
paramters