Inkscape OpenSCAD DXF Export - update for Inkscape V0.91

The original exporter did not work for the latest Inkscape Version 0.91.

As explained in
http://wiki.inkscape.org/wiki/index.php/Notes_On_Units_Handling_in_Extensions_in_0.91
a reference in the source files had to be changed to get it working.

find attached an updated version of the extension pack. Just unzip and copy to your local inkscape extension folder.

NOTE: I observed that some times the conversion of units is done correctly only if the inkscape drawing is first exported by