amqp_<filename> is used in at least two other C/C++ projects related
to amqp, so this commit changes all our source to use a qamqp header.
This avoids potential clashes, and is more in line with Qt style
Though it's not necessarily recommended (per spec), Channels can be
shared by multiple Exchanges and Queues. I've added a test here showing
that's possible with QAMQP
Matt Broadstone