Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Doc/tools/sgmlconv/esistools.py b/Doc/tools/sgmlconv/esistools.py
index b9c029b..833fea1 100644
--- a/Doc/tools/sgmlconv/esistools.py
+++ b/Doc/tools/sgmlconv/esistools.py
@@ -29,7 +29,7 @@
             n, s = s.split(";", 1)
             r = r + unichr(int(n))
         else:
-            raise ValueError, "can't handle " + `s`
+            raise ValueError, "can't handle %r" % s
     return r
 
 
@@ -220,8 +220,8 @@
             return self._decl_handler
 
         else:
-            raise xml.sax.SAXNotRecognizedException("unknown property %s"
-                                                    % `property`)
+            raise xml.sax.SAXNotRecognizedException("unknown property %r"
+                                                    % (property, ))
 
     def setProperty(self, property, value):
         if property == xml.sax.handler.property_lexical_handler: