Deprecations

**Forking Worker**

I have been benchmarking this code and I can't find a good reason to keep it around. It offer nothing in terms of parallelization. The only benefit I see it having is that it can potentially shield the parent process from jobs that leak memory. I don't think queue_classic should be held responsible for solving the leaking memory problem.

**LISTEN/NOTIFY**

The queue_classic docs state that only postgres >= 9.0 is supported. LISTEN/NOTIFY have been in postgres since 8.1. There is no reason why you wouldn't want to use this feature. This feature is currently broken and so I propose that the next version of queue_classic not only fixes the bug but makes LISTEN/NOTIFY the primary path.

Any objections?