JGroups protocol stacks need to have FC.ignore_synchronous_response set to "true"

See JGRP-928 for underlying problem. To take advantage of the fix that will come with JGroups 2.6.9 all protocol stacks that use FC must set ignore_synchronous_response="true". The default is false, which makes the fix non-functional.

This property was exposed in the JGroups 2.6.8 that Branch_5_x is currently using, so I'll go ahead and change the configs now even though they won't result in the problem going away until we move to JGroups 2.6.9.