[1.6.x] Fixed #21551 -- Reenabled loading fixtures from subdirectory

This was a regression in Django 1.6 that was only partially
restored in 839940f27f.
Thanks Jonas Haag for the report.
Backport of 41ebc4838d from master.

tests/fixtures_regress/fixtures_1/inner/absolute.json

@@ -0,0 +1,9 @@
+[
+    {
+        "pk": "1",
+        "model": "fixtures_regress.absolute",
+        "fields": {
+            "name": "Load Absolute Path Test"
+        }
+    }
+]

tests/fixtures_regress/tests.py

@@ -2,6 +2,7 @@
 # Unittests for fixtures.
 from __future__ import absolute_import, unicode_literals
 
+import json
 import os
 import re
 import warnings
@@ -19,12 +20,13 @@ from django.utils.encoding import force_text
 from django.utils._os import upath
 from django.utils import six
 from django.utils.six import PY3, StringIO
-import json
 
 from .models import (Animal, Stuff, Absolute, Parent, Child, Article, Widget,
     Store, Person, Book, NKChild, RefToNKChild, Circle1, Circle2, Circle3,
     ExternalDependency, Thingy)
 
+_cur_dir = os.path.dirname(os.path.abspath(upath(__file__)))
+
 
 class TestFixtures(TestCase):
 
@@ -150,12 +152,11 @@ class TestFixtures(TestCase):
         )
         self.assertEqual(Absolute.objects.count(), 1)
 
-    def test_relative_path(self):
-        directory = os.path.dirname(upath(__file__))
-        relative_path = os.path.join('fixtures', 'absolute.json')
+    def test_relative_path(self, path=['fixtures', 'absolute.json']):
+        relative_path = os.path.join(*path)
         cwd = os.getcwd()
         try:
-            os.chdir(directory)
+            os.chdir(_cur_dir)
             management.call_command(
                 'loaddata',
                 relative_path,
@@ -165,6 +166,10 @@ class TestFixtures(TestCase):
             os.chdir(cwd)
         self.assertEqual(Absolute.objects.count(), 1)
 
+    @override_settings(FIXTURE_DIRS=[os.path.join(_cur_dir, 'fixtures_1')])
+    def test_relative_path_in_fixture_dirs(self):
+        self.test_relative_path(path=['inner', 'absolute.json'])
+
     def test_path_containing_dots(self):
         management.call_command(
             'loaddata',
@@ -412,8 +417,6 @@ class TestFixtures(TestCase):
                 verbosity=0,
             )
 
-    _cur_dir = os.path.dirname(os.path.abspath(upath(__file__)))
-
     @override_settings(FIXTURE_DIRS=[os.path.join(_cur_dir, 'fixtures_1'),
                                      os.path.join(_cur_dir, 'fixtures_2')])
     def test_loaddata_forward_refs_split_fixtures(self):