IW.rollback has logic to make sure only one thread actually gets to do
the rollback whenever multiple threads are calling it at the same
time, by setting the "boolean closing" to true in the thread that got
Other threads wait for that variable to become false again before
returning from abort.
But, we are not restoring closing to false in a try/finally in
rollback(), which means on hitting an exception in rollback, a
subsequent call to rollback() will hang forever.
close() has the same logic, but there is already a try/finally there
to restore closing to false on exception.
The fix is straightforward.