Revision 1989

Unify the filenames stored in .thuban files so that the .thuban
files are more platform independend

* Thuban/Model/save.py (unify_filename): New. Unify filenames so
that they can be used on both windows and unix
(SessionSaver.prepare_filename): New. Handle all filename
transformations for filenames stored in the thuban file
(SessionSaver.write_data_containers, SessionSaver.write_layer):
Use prepare_filename

* test/test_save.py (SaveSessionTest.testSingleLayer)
(SaveSessionTest.testLayerProjection)
(SaveSessionTest.testRasterLayer)
(SaveSessionTest.testClassifiedLayer)
(SaveSessionTest.test_dbf_table)
(SaveSessionTest.test_joined_table): Filenames are always stored
with slashes on all currently supported platforms so adapt all
tests to this

* test/test_load.py (LoadSessionTest.filenames): With the new
filename scheme the filenames in the tests should be
understandable on all currently supported platforms so we turn
this into an empty list because we don't have to normalize them
anymore