Concurrently executing connections are allowed to use the same client ID

Section 4.3.2 of the JMS spec says that the JMS provider
should prevent concurrently executing clients from using the same client id.

Qpid JMS client allows two connections to be created using the same client id.

How reproducible:
Always

Steps to Reproduce:
1. Create two connections with the same client ID.
2. Observe that there are no exceptions being thrown.

Actual results:
No exception being thrown.

Expected results:
An exception should be thrown.