Erlang-inspired improvements to amqplib

I've been reading Joe Armstrong's Programming Erlang book, and it's been a real eye-opener. I've been intrigued by functional programming languages like Haskell and OCaml for some time, but it's been hard seeing how they'd be used for real programs, instead of just silly little factorial or quicksort examples. Joe's book is awfully well written and gives lot of very clear examples, so now when I look at bits of code like RabbitMQ, it doesn't seem like a bunch of gibberish :)

Haven't finished the book yet, but one thing I picked up from it already was the interesting way Erlang handles messages sent to processes, in how they're pattern-matched and saved for later if they're not what the process is looking for right at that moment.

At the heart of amqplib versions 0.3 or lower is a terrible mess that tries to deal with waiting for particular AMQP frames. Previously it would raise exceptions in some situations when it really shouldn't have. Specifically: if you had called basic_consume on a channel, and then called some other synchronous method like another basic_consume call - while it was expecting a basic_consume_ok response a basic_deliver could arrive and the library would raise an Exception because that wasn't expected.

A lame workaround is to use the nowait option most calls have, but I've now reworked things, cleaning up a lot of ugly code, and saving unexpected messages for later, similar to how Erlang does it. So now I believe the client library behaves in the way you'd generally expect. The improved code is currently in the Mercurial repository, and will be put out as a new release after it's had a chance to settle.