Revision 1599

Fix some bugs in Thuban and the test suite that were uncovered by
changes introduced in Python 2.3:

* Thuban/Model/table.py (DBFTable.__init__): Make sure the
filename is an absolute name

* Thuban/Model/layer.py (RasterLayer.__init__): Make sure the
filename is an absolute name

* test/test_save.py (SaveSessionTest.testRasterLayer): Use a
unique filename to save to and use the correct relative filename
in the expected output.
(SaveSessionTest.test_dbf_table): Use the correct relative
filename in the expected output.

* test/test_layer.py (TestLayer.test_raster_layer): Update the
test to check whether the filename is absolute.