Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/nntplib.py b/Lib/nntplib.py
index 6299ba2..83544b8 100644
--- a/Lib/nntplib.py
+++ b/Lib/nntplib.py
@@ -175,7 +175,7 @@
         If the response code is 200, posting is allowed;
         if it 201, posting is not allowed."""
 
-        if self.debugging: print '*welcome*', `self.welcome`
+        if self.debugging: print '*welcome*', repr(self.welcome)
         return self.welcome
 
     def set_debuglevel(self, level):
@@ -190,12 +190,12 @@
     def putline(self, line):
         """Internal: send one line to the server, appending CRLF."""
         line = line + CRLF
-        if self.debugging > 1: print '*put*', `line`
+        if self.debugging > 1: print '*put*', repr(line)
         self.sock.sendall(line)
 
     def putcmd(self, line):
         """Internal: send one command to the server (through putline())."""
-        if self.debugging: print '*cmd*', `line`
+        if self.debugging: print '*cmd*', repr(line)
         self.putline(line)
 
     def getline(self):
@@ -203,7 +203,7 @@
         Raise EOFError if the connection is closed."""
         line = self.file.readline()
         if self.debugging > 1:
-            print '*get*', `line`
+            print '*get*', repr(line)
         if not line: raise EOFError
         if line[-2:] == CRLF: line = line[:-2]
         elif line[-1:] in CRLF: line = line[:-1]
@@ -213,7 +213,7 @@
         """Internal: get a response from the server.
         Raise various errors if the response indicates an error."""
         resp = self.getline()
-        if self.debugging: print '*resp*', `resp`
+        if self.debugging: print '*resp*', repr(resp)
         c = resp[:1]
         if c == '4':
             raise NNTPTemporaryError(resp)