Fixes non-linear startup time increase for large folders

lib/helper.js

@@ -13,16 +13,16 @@ helper.isDir = function isDir (dir) {
 
 // Create a `key:[]` if doesnt exist on `obj` then push or concat the `val`
 helper.objectPush = function objectPush (obj, key, val) {
-  if (obj[key] == null) {
-    obj[key] = [];
+  var arr = obj[key];
+  if (arr == null) {
+    obj[key] = arr = [];
   }
   if (Array.isArray(val)) {
-    obj[key] = obj[key].concat(val);
-  } else if (val) {
-    obj[key].push(val);
+    obj[key] = arr = helper.unique(arr, val);
+  } else if (val && arr.indexOf(val) === -1) {
+    arr.push(val);
   }
-  obj[key] = helper.unique(obj[key]);
-  return obj[key];
+  return arr;
 };
 
 // Ensures the dir is marked with path.sep