Replaced variable o with obj in operator.rst because o is easy to
confuse.
Added a note about Python 3's collections.Mapping etc., above section
that describes isMappingType() etc.
Added xrefs between os, os.path, fileinput, and open().
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index a7f8118..7f03a75 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -8,9 +8,10 @@
This module provides a more portable way of using operating system dependent
functionality than importing a operating system dependent built-in module like
-:mod:`posix` or :mod:`nt`. (If you just want to read or write a file see
-:func:`open`, and if you want to manipulate paths, see the :mod:`os.path`
-module.)
+:mod:`posix` or :mod:`nt`. If you just want to read or write a file see
+:func:`open`, if you want to manipulate paths, see the :mod:`os.path`
+module, and if you want to read all the lines in all the files on the
+command line see the :mod:`fileinput` module.
This module searches for an operating system dependent built-in module like
:mod:`mac` or :mod:`posix` and exports the same functions and data as found