Correct check mode for pip in virtualenv.

Fix #412.  Check mode was always returning changed=True for pip
when the target was in a virtualenv.  The code now uses the normal
tests for determining if change status.

packaging/language/pip.py

@@ -314,7 +314,7 @@ def main():
         this_dir = os.path.join(this_dir, chdir)
 
     if module.check_mode:
-        if env or extra_args or requirements or state == 'latest' or not name:
+        if extra_args or requirements or state == 'latest' or not name:
             module.exit_json(changed=True)
         elif name.startswith('svn+') or name.startswith('git+') or \
                 name.startswith('hg+') or name.startswith('bzr+'):