Require virtualenv 1.7 for running tests, and drop --no-site-packages.

setup.py

@@ -51,5 +51,5 @@ setup(name="pip",
       packages=['pip', 'pip.commands', 'pip.vcs'],
       entry_points=dict(console_scripts=['pip=pip:main', 'pip-%s=pip:main' % sys.version[:3]]),
       test_suite='nose.collector',
-      tests_require=['nose', 'virtualenv>=1.6', 'scripttest>=1.1.1', 'mock'],
+      tests_require=['nose', 'virtualenv>=1.7', 'scripttest>=1.1.1', 'mock'],
       zip_safe=False)

tests/test_pip.py

@@ -54,7 +54,7 @@ def create_virtualenv(where, distribute=False):
     try:
         import virtualenv
         distribute_opt = distribute and ['--distribute'] or []
-        sys.argv = ['virtualenv', '--quiet'] + distribute_opt + ['--no-site-packages', '--unzip-setuptools', where]
+        sys.argv = ['virtualenv', '--quiet'] + distribute_opt + ['--unzip-setuptools', where]
         virtualenv.main()
     finally:
         sys.argv = save_argv