Refs #2027. Fixed sort order assumption.

lib/pipeline/documentSources/DocumentSource.js

@@ -218,7 +218,7 @@ public:
             bb._id = 0;
 
         var last = "";
-        Object.keys(deps).forEach(function(it){
+        Object.keys(deps).sort().forEach(function(it){
             if (last !== "" && it.slice(0, last.length) === last){
                 // we are including a parent of *it so we don't need to
                 // include this field explicitly. In fact, due to