provide better error message for unknown globals (copied from CPython)

--HG--
rename : tests/broken/ref2global.pyx => tests/run/ref2global.pyx

Cython/Utility/ObjectHandling.c

@@ -595,7 +595,12 @@ static PyObject *__Pyx_GetName(PyObject *dict, PyObject *name) {
             result = __Pyx_PyObject_GetAttrStr($builtins_cname, name);
         }
         if (!result) {
-            PyErr_SetObject(PyExc_NameError, name);
+            PyErr_Format(PyExc_NameError,
+#if PY_MAJOR_VERSION >= 3
+                "global name '%U' is not defined", name);
+#else
+                "global name '%s' is not defined", PyString_AS_STRING(name));
+#endif
         }
     }
     return result;

tests/broken/ref2global.pyx

-def f(a):
-    a = f
-    a = g
-

tests/run/ref2global.pyx

+# mode: run
+# tag: global, nameerror
+
+try:
+    from heapq import *   # just to confuse the compiler
+except ImportError:
+    pass
+
+
+def f(a):
+    """
+    >>> f(1)
+    Traceback (most recent call last):
+    NameError: global name 'definitely_unknown_name' is not defined
+    """
+    a = f
+    a = definitely_unknown_name