[Radiant] import_export patches for user errors (and extensions)

[Giovanni Intini]

Since this is the second time this week someone had problems with the
import_export extension, I will post my patches.

Use them at your own risk, they have been tested only by Andrea Franz,
Will Green and me. I won't post them to the dev site until I have the
time to really look into them and clean 'em up.

Good luck,
Giovanni :)