SYSML17 — NoBuffer: Clarify when a token is considered "refused"

The SysML specification says (section 11.3.2.4, description sub-clause):
"tokens arriving at the node are discarded if they are refused by outgoing edges"

But the condition fro considering that a token is "refused" is specified neither in that specification nor in the UML specification.

Proposal:
Assume that a token is refused when its availability has been checked by an action that has an edge incoming from the node where this token is stored but not accepted by this action, whatever the reason.