Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/opcode.py b/Lib/opcode.py
index cfde5f8..39d4bd2 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -21,7 +21,7 @@
 
 opmap = {}
 opname = [''] * 256
-for op in range(256): opname[op] = '<' + `op` + '>'
+for op in range(256): opname[op] = '<%r>' % (op,)
 del op
 
 def def_op(name, op):