PropagationContextManager.getTransactionPropagationContext() to log returned tpc

From a support point of view, it'd be really helpful if the JTA
and JTS PropagationContextManager logged which tcp is
returned when getTransactionPropagationContext() is called.

I have done a local patch for the JTA version as a result of trying
to figure out how it worked internally:

public Object getTransactionPropagationContext()
{
if (log.isDebugEnabled())

{ log.debug("PropagationContextManager.getTransactionPropagationContext - called"); }

String txid = ((BasicAction.Current() == null) ? null : BasicAction.Current().get_uid().stringForm());

if (log.isDebugEnabled())

{ log.debug("PropagationContextManager.getTransactionPropagationContext - returned tpc = " + txid); }

return txid;
}

If everyone's happy with this, I can commit it myself. Thoughts?