Revision 984

Implement a way to discover dependencies between tables and
shapestores.

* Thuban/Model/transientdb.py (TransientTableBase.Dependencies)
(TransientJoinedTable.Dependencies)
(AutoTransientTable.SimpleQuery): New. Implement the dependencies
interface
(TransientJoinedTable.__init__): Keep tack of the original table
objects in addition to the corresponding transient tables.

* Thuban/Model/table.py (DBFTable.Dependencies)
(MemoryTable.Dependencies): New. Implement the dependencies
interface

* Thuban/Model/data.py (ShapeTable): New. Helper class for
ShapefileStore
(ShapefileStore.__init__): Use ShapeTable instead of
AutoTransientTable
(ShapefileStore.Table, ShapefileStore.Shapefile): Add doc-strings
(ShapefileStore.FileName, ShapefileStore.FileType): New. Accessor
methods for filename and type
(ShapefileStore.Dependencies): New. Implement the dependencies
interface
(DerivedShapeStore): New class to replace SimpleStore. The main
difference to SimpleStore is that it depends not on a shapefile
but another shapestore which expresses the dependencies a bit
better
(SimpleStore.__init__): Add deprecation warning.

* test/test_dbf_table.py (TestDBFTable.test_dependencies): New.
Test for the Dependencies method.

* test/test_memory_table.py (TestMemoryTable.test_dependencies):
New. Test for the Dependencies method.

* test/test_transientdb.py
(TestTransientTable.test_auto_transient_table_dependencies): New.
Test for the Dependencies method.
(TestTransientTable.test_transient_joined_table): Add test for the
Dependencies method.

* test/test_session.py (TestSessionSimple.setUp)
(TestSessionSimple.tearDown): New. Implement a better way to
destroy the sessions.
(TestSessionSimple.test_initial_state)
(TestSessionSimple.test_add_table): Bind session to self.session
so that it's destroyed by tearDown
(TestSessionSimple.test_open_shapefile): New. Test for
OpenShapefile and the object it returns