Moved the #require runway and tower declarations below the AIRPORT object literal.
Added message handling on takeoffs in order to send and stop running the code.
Added a #land method to call when receiving jsPlanes from other airports.
Added message handling to receive and start running a jsPlane.
Modified #prependCalls to return immediately if a string function is supplied.
Supplied the jsPlane's ID property on calls to jsfly#crash using this.id.