Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Demo/scripts/from.py b/Demo/scripts/from.py
index d61afde..3c04fcd 100755
--- a/Demo/scripts/from.py
+++ b/Demo/scripts/from.py
@@ -31,5 +31,5 @@
             if not line or line == '\n':
                 break
             if line.startswith('Subject: '):
-                print `line[9:-1]`,
+                print repr(line[9:-1]),
         print