NO-JIRA: demonstrate that two concurrent send.c implementations cannot talk to one recv.c

testcase:

Sample recv output: (Note how the output is serialized, all messages from one, then all messages from the other)

Address: amqp://0.0.0.0
Subject: Greetings from send 4428
Content: "Hello World!"
Address: amqp://0.0.0.0
Subject: Greetings from send 4428
Content: "Hello World, part 2!"
Address: amqp://0.0.0.0
Subject: Greetings from send 4428
Content: "Oh no! More Hello World!"
Address: amqp://0.0.0.0
Subject: Greetings from send 4427
Content: "Hello World!"
Address: amqp://0.0.0.0
Subject: Greetings from send 4427
Content: "Hello World, part 2!"
Address: amqp://0.0.0.0
Subject: Greetings from send 4427
Content: "Oh no! More Hello World!"