Description of problem:
After a backup disconnects from a primary, it will attempt to destroy any auto-delete queues.  However, if an auto-delete queue has a timeout of zero seconds set, the HA broker will deadlock holding a reader lock to the exchange registry while attempting to acquire a writer lock.

Version-Release number of selected component (if applicable):
Qpid 0.18-6

How reproducible:
100%

Steps to Reproduce:
1. Create an auto-delete queue w/ an auto-delete timeout of zero seconds
2. Disconnect the backup from the primary
  
Actual results:
The backup broker deadlocks

Expected results:
The backup broker does not deadlock

Workaround:
Never set the auto-delete timeout attribute if the timeout is zero seconds