Chunk up payload into discrete Body frames

During Tune/Ok a frame_max is negotiated. The server will drop connections that
publish larger payloads than this. Use this frame_max to slice up the payload
into appropriately sized Body frames.
negotiate tune parameters with the server
simplify body fragmenting
test messages are getting chunked up
use negotiated channel_max
Changelog
Checking in changes prior to tagging of version 1.17.

Changelog diff is:

diff --git a/Changes b/Changes
index 6e7276e..5578b4e 100644
--- a/Changes
+++ b/Changes
@@ -1,5 +1,6 @@
 Revision history for Perl extension AnyEvent::RabbitMQ

+1.17  Fri Jul 25 14:02:00 PDT 2014
         - Add support for chunking large bodies into multiple AMQP frames,
           allowing the sending of large messages.