add a py.test placeholder setup that errors out when trying to get installed

(this is registered at pypi.python.org already)

extra/setup-py.test/setup.py

@@ -0,0 +1,11 @@
+import sys
+from distutils.core import setup
+
+if __name__ == "__main__":
+    if "sdist" not in sys.argv[1:]:
+        raise ValueError("please use 'pytest' pypi package instead of 'py.test'")
+    setup(
+        name="py.test",
+        version="0.0",
+        description="please use 'pytest' for installation",
+    )