Merge lp://staging/~free.ekanayaka/txamqp/synchronous-testing-helpers into lp://staging/txamqp

This adds a new txamqp.testing.AMQPump class which can use as a fake AMQP transport for writing synchronous unit tests in a convenient way. Example:

client = AMQClient(...)
transport = AMQPump()
transport.connect(client)
channel = self.successResultOf(client.channel(1))
d = clientChannel.basic_consume(queue="test-queue")
transport.channel(1).basic_consume_ok(consumer_tag="consumer")
self.assertTrue(self.successResultOf(d))

The branch also fixes a small bug in txamqp.factory.AMQFactory where newly built protocols were not passed a fresh TwistedDelegate.

It also moves the DEFAULT_SPEC constant from txamqp.factory to txamqp.spec
which seems a better fit.

Finally it makes AMQClient pass its clock to callLater, for easier synchronous testing.