UML14 — Control pins

There should be a special kind of pin for control tokens. This will
allow parameter sets to be used with control, for example. Also
resolves issue of where control is bufferred when it is direceted at a
join. Can be implemented as a pin that has no parameter, by making them
the last in the ordering of pins, so no parameter corresponds to them.
This is also a request of the SysML team.

see above