Dispose the stream if last subscriber terminates.

[CihanSari]

In our workflow server is streaming until nobody is listening to. We don't get this information with the current observable. I had to fix this issue in a very similar fashion to this pull request at work. I have tried to isolate the necessary change to address the issue. I did not test the changes, especially because I have updated the rxjs requirement at work, and this meant a complete different interface. I hope this patch delivers the "no more subscribers" information to stream source.

[kondi]

Hi!

Thanks for the finding! What does the finally operator help in this case? Can't we just return a call to cancel as unsubscribe function from the Observable factory function?

[CihanSari]

Hi kondi!

Yes, that would be a solution. My old PR had the issue with canceling the call prematurely on first subscriber's unsubscription. I have merged the changes that I made for work and updated the PR. I had to clean A LOT OF code, and I couldn't test this version if it works, yet. However, I hope it gives you the idea.

Main decision to make is whether or not to replay the stream on consecutive subscribers to the shared observable.

[CihanSari]

This solves only half the problem, as our server still keeps publishing without any care on the call status.