[RFE] business rule task supports boundary error event

Our documentation suggests to use the boundary error event for handling the exception occurred in a workflow process.
If a boundary error event is used for a business rule task the following exception is thrown:
java.lang.ClassCastException: org.jbpm.workflow.core.node.RuleSetNode cannot be cast to org.jbpm.process.core.ContextContainer

Initially support for boundary events was only for state nodes - those that can stop in certain node. This was mainly for the catch events like signal or message - as if the node is not going to stop and just run through like script task there is no way to send a signal to it. Though error events are bit different and thus makes sense to have them supported.

Please add the new feature that the business rule task could support the boundary error event in a workflow process.