add channel.channel based on coros.queue(0) (temporarily for backward compatibility)

eventlet/channel.py

@@ -0,0 +1,15 @@
+from eventlet import coros
+
+class channel(coros.queue):
+
+    def __init__(self):
+        coros.queue.__init__(self, 0)
+
+    def receive(self):
+        return self.wait()
+
+    @property
+    def balance(self):
+        return self.sem.balance
+
+