Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Doc/tools/cvsinfo.py b/Doc/tools/cvsinfo.py
index 58a32c2..cc90fe5 100644
--- a/Doc/tools/cvsinfo.py
+++ b/Doc/tools/cvsinfo.py
@@ -78,4 +78,4 @@
         return fn[len(self.cvsroot_path)+1:]
 
     def __repr__(self):
-        return "<RepositoryInfo for %s>" % `self.get_cvsroot()`
+        return "<RepositoryInfo for %r>" % self.get_cvsroot()