[api] Load sources into the default system store so they are permenantly cached

lib/nconf/provider.js

@@ -292,8 +292,7 @@ Provider.prototype.merge = function () {
 //
 Provider.prototype.load = function (callback) {
   var self = this,
-      stores = this._stores.map(function (name) { return self[name] })
-                           .concat(this.sources);
+      stores = this._stores.map(function (name) { return self[name] });
   
   function loadStoreSync(store) {
     if (!store.loadSync) {
@@ -313,18 +312,52 @@ Provider.prototype.load = function (callback) {
       : store.load(next);
   }
   
+  function loadBatch (targets, done) {
+    if (!done) {
+      return common.merge(targets.map(loadStoreSync));
+    }
+
+    async.map(targets, loadStore, function (err, objs) {
+      return err ? done(err) : done(null, common.merge(objs));
+    });
+  }
+  
+  function mergeSources (data) {
+    //
+    // If `data` was returned then merge it into 
+    // the system store.
+    //
+    if (data && typeof data === 'object') {
+      Object.keys(data).forEach(function (key) {
+        self.system.merge(key, data[key]);
+      });
+    }
+  }
+  
+  function loadSources () {
     //
     // If we don't have a callback and the current 
     // store is capable of loading synchronously
     // then do so.
     //
     if (!callback) {
-    return common.merge(stores.map(loadStoreSync));
+      mergeSources(loadBatch(self.sources));
+      return loadBatch(stores);
     }
     
-  async.map(stores, loadStore, function (err, objs) {
-    return err ? callback(err) : callback(null, common.merge(objs));
+    loadBatch(self.sources, function (err, data) {
+      if (err) {
+        return callback(err);
+      }
+      
+      mergeSources(data);
+      return loadBatch(stores, callback);
     });
+  }
+  
+  return self.sources.length 
+    ? loadSources()
+    : loadBatch(stores, callback);
 };
 
 //