This allows a derived (concrete) implementation to share information (e.g. sample rate, buffer size)
between the audio backend side of things and the port management side of things.
every session member is now initialized using C++ constructor syntax
session construction reordered to clarify the split(s) between work
where the engine is not relevant and work where is it is. this
split is still not 100% obvious, but is enormously clearer than
previously.
if engine/backend are not running as session is created, and the SR
of the sample rate is known, attempt to force backend to that value.
the goal is to allow a clear demarcation of where we need
the audioengine and have existing data parameters (e.g. sample rate)
for the session so that we can coerce the engine (if possible)
to match to session values.
also, to rationalize construction even more and use C++
constructor syntax as much as possible.
Issues remain with the basic model of the AMS dialog - when is
newly chosen state pushed into the backend (which can then
modify the control app button sensitivity. This is a special
problem for this button because APIs like ASIO and CoreAudio
probably don't allow us to launch a control app for an arbitrary
device, but only one actually in use. In this sense it is
different from properties like available buffer size etc, where
we can typically query without actually using the device.
This was caused by using jack_port_get_connections() which will
not return the correct status for ports owned by another JACK
client. Because of the potential for deadlock by calling
jack_port_get_all_connections(), an extra argument was added
to several PortEngine:: API calls to specify whether the call
is in a process-callback context, which defaults to true.
The only place where false is passed is within the GlobalPortMatrix
when we need to determine whether two non-ardour ports are
connected.
This makes the responsibilities and ownership of non-Route related MIDI ports
more clear, and removes a few wierd bits of code. It also ensures that open/close/open
on the same session will retain connections for those MIDI ports
