[PATCH] Move polygon creation from rect attrs into helper method

[Christina Roßmanith]

Hi,

if the corner radii-patch is fine, this patch moves the translation of 
rectangle attributes into a polygon into a helper method. Works fine 
here, but a short review would be nice.

@Thorsten: The method importSVG which calls the ShapeRenderingVisitor is 
used for magic file type detection?

Christina