[Fixes ##98959702] Plus sign drop target was not showing up in graph when there were multiple targets. This was because the target's idea of the other attribute description was not being kept current. Now it is.
[Fixes ##98959702] Plus sign drop target was not showing up in graph when there were multiple targets. This was because the target's idea of the other attribute description was not being kept current. Now it is.

concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap