FileStorageTests.tearDown(): Conditionalize the use of waitpid since

Windows doesn't have it until Python 2.3

src/ZEO/tests/testZEO.py

@@ -142,6 +142,8 @@ class FileStorageTests(GenericTests):
         self._storage.close()
         for server in self._servers:
             forker.shutdown_zeo_server(server)
+        if hasattr(os, 'waitpid'):
+            # Not in Windows Python until 2.3
             for pid in self._pids:
                 os.waitpid(pid, 0)