The 0.6.0 version of librabbitmq-c added two parameters to amqp_exchange_declare
which allow auto-deleted and internal exchanges. This change requires more
advanced version detection so that code could be conditionally compiled for
newer versions of the library.
The mqfilter was not built by default even though it should have been. This has
been fixed but the filter is built only if librabbitmq is found. This was done
to avoid having the librabbitmq and its development headers as a hard
dependency.