Description of problem:
Validator marks boundary event by alert "Node has no incoming connection". For the boundary event, there is an attribute "attachedToRef" instead of attribute "incoming connection". From BPMN 2 definition: "If the Intermediate Event is attached to the boundary of an Activity then the Intermediate Event MUST NOT be a target for a Sequence Flow; it cannot have an incoming Sequence Flows."


Version-Release number of selected component (if applicable):
BRMS 5.3.1 ER1(ER2) and designer 2.3.1-DEV

How reproducible:
When attach any event to activity as boundary event

Steps to Reproduce:
 1. clear a repository (or import idle repository)
 2. create new process (call sub-process)
       Start->Task->XORgateway->End
                        |->Error
 3. validate process (create PNG, set property "ErrorRef" for Error End Event)
 4. save and close process
 5. create new process (call boundaryevent)
       Start->ReusableSubprocess With BoundaryEvent->End
 6. create PNG image, set property "ErrorRef" for boundary error event, set property "Called Element" for Reusable Subprocess
 7. validate
  
Actual results:
Validation marks boundary event

Expected results:
Alert "There are no validation errors"

Additional info:
<bpmn2:boundaryEvent xmlns:bpmn2="http://www.omg.org/spec/BPMN/20100524/MODEL" id="_88B653A2-3371-40BC-A100-28CF073B7256" drools:bgcolor="#f5deb3" xmlns:drools="http://www.jboss.org/drools" drools:selectable="true" drools:bordercolor="#a0522d" drools:boundaryca="false" name="" attachedToRef="_F206DAF8-C0B6-4D9B-A1EC-DB381B0A1F96" cancelActivity="false">
      <bpmn2:outgoing>_C85DB60A-72BB-40FC-85EE-7634269409CF</bpmn2:outgoing>
      <bpmn2:errorEventDefinition id="_yThN4RIgEeKS37fzgw701A" errorRef="_yThN4hIgEeKS37fzgw701A"/>
    </bpmn2:boundaryEvent>