Check type of onException argument to bindEnvironment

Meteor.bindEnvironment() can have an invalid error handler accidentally
passed as the second argument, especially in CoffeeScript where the
issue is not easy to find. This can cause a cryptic error message about
an exception being thrown when onException() itself is being called.

packages/meteor/dynamics_nodejs.js

@@ -94,6 +94,8 @@ Meteor.bindEnvironment = function (func, onException, _this) {
         error && error.stack || error
       );
     };
+  } else if (typeof(onException) !== 'function') {
+    throw new Error('onException argument must be a function, string or undefined for Meteor.bindEnvironment().');
   }
 
   return function (/* arguments */) {