Revision 723

First step towards table management. Introduce a simple data
abstraction so that we replace the data a layer uses more easily
in the next step.

* Thuban/Model/data.py: New file with a simple data abstraction
that bundles shapefile and dbffile into one object.

* Thuban/Model/session.py (Session.OpenShapefile): New method to
open shapefiles and return a shape store object

* Thuban/Model/layer.py (Layer.__init__): Pass the data as a store
object instead of a shapefile filename. This introduces a new
instance variable store holding the datastore. For intermediate
backwards compatibility keep the old instance variables.
(open_shapefile): Removed. No longer needed with the shape store.
(Layer.SetShapeStore, Layer.ShapeStore): New methods to set and
get the shape store used by a layer.
(Layer.Destroy): No need to explicitly destroy the shapefile or
table anymore.

* Thuban/UI/mainwindow.py (MainWindow.AddLayer)
(MainWindow.AddLayer): Use the session's OpenShapefile method to
open shapefiles

* Thuban/Model/load.py (ProcessSession.start_layer): Use the
session's OpenShapefile method to open shapefiles

* test/test_classification.py
(TestClassification.test_classification): Use the session's
OpenShapefile method to open shapefiles and build the filename in
a more platform independed way

* test/test_layer.py (TestLayer.setUp, TestLayer.tearDown):
Implement to have a session to use in the tests
(TestLayer.test_arc_layer, TestLayer.test_polygon_layer)
(TestLayer.test_point_layer, TestLayer.test_empty_layer): Use the
session's OpenShapefile method to open shapefiles
(TestLayerLegend.setUp): Instantiate a session so that we can use
it to open shapefiles.
(TestLayerLegend.tearDown): Make sure that all references to
layers and session are removed otherwise we may get a resource
leak

* test/test_map.py (TestMapAddLayer.test_add_layer)
(TestMapWithContents.setUp): Instantiate a session so that we can
use it to open shapefiles.
(TestMapWithContents.tearDown): Make sure that all references to
layers, maps and sessions are removed otherwise we may get a
resource leak
("__main__"): use support.run_tests() so that more info about
uncollected garbage is printed

* test/test_save.py (SaveSessionTest.testSingleLayer): Use the
session's OpenShapefile method to open shapefiles
("__main__"): use support.run_tests() so that more info about
uncollected garbage is printed

* test/test_selection.py (TestSelection.tearDown): Make sure that
all references to the session and the selection are removed
otherwise we may get a resource leak
(TestSelection.get_layer): Instantiate a session so that we can
use it to open shapefiles.
("__main__"): use support.run_tests() so that more info about
uncollected garbage is printed

* test/test_session.py (TestSessionBase.tearDown)
(TestSessionWithContent.tearDown): Make sure that all references
to the session and layers are removed otherwise we may get a
resource leak
(TestSessionWithContent.setUp): Use the session's OpenShapefile
method to open shapefiles