[Etoys] Possible bug with etoy tile variables

[Karl Ramberg]

When I create a script with a variable assignment I can't replace the 
variable tile with another.

To reproduce make two variables for a morph.
Make a assignment script for  one of them.
Pull out the name part of the second variable and try to drop it on the 
name part of the one in the script.

This bug makes it hard to refactor scripts and experiment, because you 
have to recreate the whole tile row to change just the assignment.

Karl