Bind BeanManager to JNDI when naming context is read/write (as in JBoss AS/EAP 5)

It's possible for the Weld servlet listener to be proactive and bind the BeanManager to JNDI when the naming context is read/write, as it is in JBoss AS and EAP 5. There's another good reason why this needs to be done. JBoss AS does not support defining naming resources in context.xml (which on JBoss AS is WEB-INF/context.xml). Therefore, there's no other way to push the BeanManager into JNDI.

The logic for this feature is pretty straightforward. Look for the BeanManager in JNDI. If it's not there, attempt to put it there. If that fails, just log a warning message that the BeanManager will not be available in JNDI.