merge this from trunk:

r58067 | gregory.p.smith | 2007-09-09 16:36:46 -0700 (Sun, 09 Sep 2007) | 22 lin
es

Change socket.error to inherit from IOError rather than being a stand
alone class.  This addresses the primary concern in

 http://bugs.python.org/issue1706815

python-dev discussion here:

 http://mail.python.org/pipermail/python-dev/2007-July/073749.html

I chose IOError rather than EnvironmentError as the base class since
socket objects are often used as transparent duck typed file objects
in code already prepared to deal with IOError exceptions.

also a minor fix:

 urllib2 - fix a couple places where IOError was raised rather than URLError.
           for better or worse, URLError already inherits from IOError so
           this won't break any existing code.

 test_urllib2net - replace bad ftp urls.

Doc/library/socket.rst

@@ -85,6 +85,9 @@ The module :mod:`socket` exports the following constants and functions:
    accompanying :exc:`os.error`. See the module :mod:`errno`, which contains names
    for the error codes defined by the underlying operating system.
 
+   .. versionchanged:: 2.6
+      :exc:`socket.error` is now a child class of :exc:`IOError`.
+
 
 .. exception:: herror