[IndexedDB] Calling setVersion while already in a setVersion transaction

What should we do when setVersion is called while a setVersion transaction
is currently active?

Off the top of my head, I can think of two behaviors we might want to spec:
 1) Have the subsequent setVersion simply throw an error.  2) Have the
subsequent setVersion adopt the existing setVersion transaction and change
the version.  (i.e. whatever the last setVersion call sets as the version
string will win.)  Any others?  What do you guys think is the most sane
behavior?

J