Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/xml/dom/domreg.py b/Lib/xml/dom/domreg.py
index 117ca49..684c436 100644
--- a/Lib/xml/dom/domreg.py
+++ b/Lib/xml/dom/domreg.py
@@ -87,7 +87,7 @@
     while i < length:
         feature = parts[i]
         if feature[0] in "0123456789":
-            raise ValueError, "bad feature name: " + `feature`
+            raise ValueError, "bad feature name: %r" % (feature,)
         i = i + 1
         version = None
         if i < length: