asyncMarshalling should be turned off by default to avoid reordering

Over the past few weeks we've discovered that having async marshalling turned on can produce some nasty reordering.

Examples include:

• http://community.jboss.org/message/553947#553947
• http://community.jboss.org/thread/154677?start=15&tstart=0

As a result of this, we're turning off async marshalling by default from 4.1 onwards