Refresh the texture drop down contents when one edits a single copy of a
decal
Add a little more protection in getElementAt because Apples' LAF
sometimes returns -1.
Improve refreshing the decal model by doing it whenever the underlying
appearance changes.  This allows for "From file" to work correctly as
well.
Merge pull request #129 from kruland2607/fixdecaldropdown

Fix for issue #116