Previously if multiple attempts to call consume were made, then
QAmqpQueue would send a frame for each of them leading to multiple
consumer tags and general confusion. This guards from calling
consume multiple times.
This is a very small library, so there is no real pressing need for
a library namespace. Further, the namespacing actually makes it rather
difficult to work with in some cases. Opting for a more "Qt" style
class naming scheme, using the QAmqp class prefix
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
Matt Broadstone