Clean-up example code: remove string module and backticks.

Doc/lib/libsmtplib.tex

@@ -264,7 +264,6 @@ processing of the \rfc{822} headers.  In particular, the `To' and
 
 \begin{verbatim}
 import smtplib
-import string
 
 def prompt(prompt):
     return raw_input(prompt).strip()
@@ -275,7 +274,7 @@ print "Enter message, end with ^D (Unix) or ^Z (Windows):"
 
 # Add the From: and To: headers at the start!
 msg = ("From: %s\r\nTo: %s\r\n\r\n"
-       % (fromaddr, string.join(toaddrs, ", ")))
+       % (fromaddr, ", ".join(toaddrs)))
 while 1:
     try:
         line = raw_input()
@@ -285,7 +284,7 @@ while 1:
         break
     msg = msg + line
 
-print "Message length is " + `len(msg)`
+print "Message length is " + repr(len(msg))
 
 server = smtplib.SMTP('localhost')
 server.set_debuglevel(1)