Description of problem:
JMS Connection.getMetaData returns a usable enumeration only 
on the first call to getMetaData. Invoking getMetaData multiple times, 
either on the same connection or even completely different connections 
results in a empty Enumeration.

To me more precise, after the first call to getMetaData, subsequent 
calls during the duration of the JVM, on any connection will return a 
empty Enumeration.

Looks like this is is a bug in the MRG client implementation. Debugging 
shows that org.apache.qpid.client.CustomJMSXProperty is used to return 
the metadata Enumeration. But the _names member in this class is static, 
which means that all connections get the same Enumeration object.

So, if someone gets the connection meta and iterates over the 
Enumeration, other connections see the same modified Enumeration as 
well. And because the Enumeration's pointer has already been advanced to 
the end, others are not able to get elements from the Enumeration.

How reproducible:
Always

Steps to Reproduce:
1. Run a client with the following code

Connection conn = factory.createConnection();
for (Enumeration meta = conn.getMetaData().getJMSXPropertyNames(); meta.hasMoreElements();)
{
  System.out.println(meta.nextElement());
}
            
System.out.println("Getting connection meta data again");
for (Enumeration meta = conn.getMetaData().getJMSXPropertyNames(); meta.hasMoreElements();)
{
  System.out.println(meta.nextElement());
}

2. Observe that the second time around nothing is printed, since the enumeration is empty.

  
Actual results:
If conn.getMetaData().getJMSXPropertyNames() is called a second time on the same connection or in a different connection (from the same JVM) an empty enumeration is returned.

Expected results:
Every time getJMSXPropertyNames() is called, a enumeration with the property names should be returned.