Implemented a load scheduler that groups tests by scope.

setup.py

@@ -1,5 +1,13 @@
+from sys import version_info
+
 from setuptools import setup, find_packages
 
+install_requires = ['execnet>=1.1', 'pytest>=3.0.0']
+
+if version_info < (2, 7):
+    install_requires.append('ordereddict')
+
+
 setup(
     name="pytest-xdist",
     use_scm_version={'write_to': 'xdist/_version.py'},
@@ -20,7 +28,7 @@ setup(
         ],
     },
     zip_safe=False,
-    install_requires=['execnet>=1.1', 'pytest>=3.0.0'],
+    install_requires=install_requires,
     setup_requires=['setuptools_scm'],
     classifiers=[
         'Development Status :: 5 - Production/Stable',