Issue 4929: smptlib.py can raise socket.error

the SMPT.getreply() method doesn't check for socket.error when doing its 
readline() call.  We now check for connection reset and others that can 
occur here and properly close.  This is to comply with the documentation 
that doesn't specify socket.error as part of the exceptions raised.

Your patch looks fine but it would be much better with a test in 
Lib/test/test_smtp.py ;-)

If you can offer a suggestion as to how to reliably trigger a 
WSAECONNRESET error on windows (or its equivalent on unix) I'll be 
happy to do that.

On Windows, if you exit a process abnormally (using e.g. os._exit() in 
Python) while it still has open connections, the other side receives a 
WSAECONNRESET (error 10054).

So, you could write a test case using a dumb server (running as another 
process) with a very short, predefined sequence of recv/send calls, 
ending abruptly with os._exit().

On Linux I *think* you would get ECONNRESET, and at least some form of 
error on other OS's.

IMHO I wouldn't test such case.
Behaviors between different platform are unpredictable.

Submitted as r68618

Note, this has been ported to py3k in http://svn.python.org/view?
view=rev&rev=68736