Backport docs for abc module to 2.6.
diff --git a/Doc/library/python.rst b/Doc/library/python.rst
index d9a37bb..e956f34 100644
--- a/Doc/library/python.rst
+++ b/Doc/library/python.rst
@@ -18,6 +18,7 @@
    __main__.rst
    warnings.rst
    contextlib.rst
+   abc.rst
    atexit.rst
    traceback.rst
    __future__.rst