Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Demo/tkinter/matt/animation-w-velocity-ctrl.py b/Demo/tkinter/matt/animation-w-velocity-ctrl.py
index a45f3f0..f3332f2 100644
--- a/Demo/tkinter/matt/animation-w-velocity-ctrl.py
+++ b/Demo/tkinter/matt/animation-w-velocity-ctrl.py
@@ -28,7 +28,7 @@
     def moveThing(self, *args):
 	velocity = self.speed.get()
 	str = float(velocity) / 1000.0
-	str = `str` + "i"
+	str = "%ri" % (str,)
 	self.draw.move("thing",  str, str)
 	self.after(10, self.moveThing)
 
diff --git a/Demo/tkinter/matt/pong-demo-1.py b/Demo/tkinter/matt/pong-demo-1.py
index dacaa38..a27f334 100644
--- a/Demo/tkinter/matt/pong-demo-1.py
+++ b/Demo/tkinter/matt/pong-demo-1.py
@@ -39,7 +39,7 @@
 	self.x = self.x + deltax
 	self.y = self.y + deltay
 
-	self.draw.move(self.ball,  `deltax` + "i", `deltay` + "i")
+	self.draw.move(self.ball,  "%ri" % deltax, "%ri" % deltay)
 	self.after(10, self.moveBall)
 
     def __init__(self, master=None):