Resolve issue 244: After the PushSharp lib (v2.1.2) is idle for 5 mins, the Channel Created and Channel Destroyed events are invoked again and again.

https://github.com/Redth/PushSharp/issues/244
Root cause: After idle timeout, the channel.Cout is zero and the codes
always satisfy the creating channel action. Then idle timeout will
destroy the new created channel and cause the create/destroy cycle.
Merge pull request #274 from JasonGit/master

Resolve issue 244: After the PushSharp lib (v2.1.2) is idle for 5 mins, ...