-bind! is now efficacious

In the [original flapjax paper](http://dl.acm.org/citation.cfm?id=1640091) they implement switchE like you have it (fig 12, p. 10), but the magic happens in the construction of **in** ; the EventStream constructor is destructive to its arguments, adding the new constructor as a sink to all sources.  So that's all I've done here.