Revision 2344

Improved the svgexport to only use unique ids. Will issues
an error message dialoge when two layer names are the same.
ShapeIDs are now added with a dash within the svg ids.

* Extensions/svgexport/svgmapwriter.py (SVGMapWriterError): New.
* Extensions/svgexport/test/test_svgmapwriter.py: Added imports
(TestSVGRenderer): New test class with test_make_in() and
test_check_for_layer_name_clash()
* Extensions/svgexport/svgmapwriter.py (SVGRenderer): Fixed __init__()
and draw_shape_layer_incrementally() to not use a baseid twice,
satisfying test_check_for_layer_name_clash()
(VirtualDC.make_id): Use a dash between baseit and id, satisfies
test_make_in().
* Extensions/svexport/svgsaver.py: Import SVGMapWriterError, wxOK
and wxICON_HAND.
(write_to_svg): Put dc and rendering in a try statement and on
catching SVGmapWriterError notify the user and delete the target file.
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