[svn r45294] Complain loudly when there is pypy without stackless

--HG--
branch : trunk

py/magic/greenlet.py

@@ -2,8 +2,10 @@ import sys
 if '_stackless' in sys.builtin_module_names:
     # when running on top of a pypy with stackless support
     from _stackless import greenlet
+elif hasattr(sys, 'pypy_objspaceclass'):
+    raise ImportError("Detected pypy without stackless support")
 else:
-    # regular CPython (or pypy without stackless support, and then crash :-)
+    # regular CPython
     import py
     gdir = py.path.local(py.__file__).dirpath() 
     path = gdir.join('c-extension', 'greenlet', 'greenlet.c')