SF Patch #494863, file.xreadlines() should raise ValueError if file is closed

This makes xreadlines behave like all other file methods
(other than close() which just returns).

Misc/NEWS

@@ -6,6 +6,10 @@ Type/class unification and new-style classes
 
 Core and builtins
 
+- file.xreadlines() now raises a ValueError if the file is closed:
+  Previously, an xreadlines object was returned which would raise
+  a ValueError when the xreadlines.next() method was called.
+
 Extension modules
 
 Library

Objects/fileobject.c

@@ -1025,6 +1025,8 @@ file_xreadlines(PyFileObject *f)
 {
 	static PyObject* xreadlines_function = NULL;
 
+	if (f->f_fp == NULL)
+		return err_closed();
 	if (!xreadlines_function) {
 		PyObject *xreadlines_module =
 			PyImport_ImportModule("xreadlines");