undo the workaround of my previous commit for "[#36443] Vertex to UV index...

undo the workaround of my previous commit for "[#36443] Vertex to UV index doesn't match with 2.68a", because that issue is fixed in blender 2.68a r59343 now.

- deleted not needed workaround for issue [#36443], because it is fixed in blender 2.68a r59343,
- added BMEdge generation to the importer (only for nice doing),
- added undo to operators,
- deleted some unused strings,