Wrap calling session close callback in Meteor.defer, so that a bunch

of connections can be closed without waiting for the close callbacks
on one connection to return before closing the other connections.

Underscore internal Session field `_closeCallbacks`.

Update comment to explain the cause of the problem requiring the use
of `Meteor.bindEnvironment` with Meteor's public API.

packages/livedata/livedata_server.js

@@ -252,7 +252,7 @@ var Session = function (server, version, socket) {
   self._pendingReady = [];
 
   // List of callbacks to call when this session is closed.
-  self.closeCallbacks = [];
+  self._closeCallbacks = [];
 
   // The `SessionHandle` for this session, passed to
   // `Meteor.server.onConnection` callbacks.
@@ -271,7 +271,7 @@ var Session = function (server, version, socket) {
           );
         }
       );
-      self.closeCallbacks.push(fn);
+      self._closeCallbacks.push(fn);
     },
     _sessionData: self.sessionData
   };
@@ -397,9 +397,10 @@ _.extend(Session.prototype, {
     // Drop the merge box data immediately.
     self.collectionViews = {};
     self.inQueue = null;
-    // XXX do we need to use Meteor.defer here as well?
-    _.each(self.closeCallbacks, function (callback) {
-      callback();
+    Meteor.defer(function () {
+      _.each(self._closeCallbacks, function (callback) {
+        callback();
+      });
     });
     Package.facts && Package.facts.Facts.incrementServerFact(
       "livedata", "sessions", -1);

packages/livedata/livedata_server_tests.js

@@ -20,10 +20,12 @@ Tinytest.addAsync(
   "livedata server - sessionHandle.close()",
   function (test, onComplete) {
 
-    // XXX I don't understand why using `bindEnvironment` here is
-    // necessary, but I get "Meteor code must always run within a
-    // Fiber. Try wrapping callbacks that you pass to non-Meteor
-    // libraries with Meteor.bindEnvironment" if I don't.
+    // XXX stream_client_nodejs.js should not be requiring a developer
+    // to use Meteor.bindEnvironment themselves when using Meteor's
+    // public API.  The problem is that the computation rerunning is
+    // triggered by the close event firing on the stream's connection
+    // object, and that callback in stream_client_nodejs.js is not
+    // wrapped in a Meteor.bindEnvironment for us.
     done = Meteor.bindEnvironment(
       function () {
         Meteor.defer(onComplete);