Fix bogus implementation of Group.bind().
Added unbind() to CanvasItem and Group classes.
diff --git a/Lib/lib-tk/Canvas.py b/Lib/lib-tk/Canvas.py
index 6eccd4d..ad0cc56 100644
--- a/Lib/lib-tk/Canvas.py
+++ b/Lib/lib-tk/Canvas.py
@@ -43,6 +43,8 @@
 		return (x1, y1), (x2, y2)
 	def bind(self, sequence=None, command=None):
 		return self.canvas.tag_bind(self.id, sequence, command)
+	def unbind(self, sequence):
+		self.canvas.tag_bind(self.id, sequence, '')
 	def config(self, cnf={}, **kw):
 		return self.canvas.itemconfig(self.id, _cnfmerge((cnf, kw)))
 	def coords(self, pts = ()):
@@ -140,8 +142,10 @@
 		self._do('addtag', 'withtag', tagOrId)
 	def bbox(self):
 		return self._getints(self._do('bbox'))
-	def bind(self, sequence=None, command=None): # XXX args?
-		return self._do('bind', sequence, command)
+	def bind(self, sequence=None, command=None):
+		return self.canvas.tag_bind(self.id, sequence, command)
+	def unbind(self, sequence):
+		self.canvas.tag_bind(self.id, sequence, '')
 	def coords(self, *pts):
 		return self._do('coords', pts)
 	def dchars(self, first, last=None):