the rest from `tools/convert_boost.sh`.
* replace boost::function, boost::bind with std::function and std::bind.
This required some manual fixes, notably std::placeholders,
some static_casts<>, and boost::function::clear -> = {}.
* Allow to exit cleanly (using access-action)
* Terminate when the backend is halted
* Handle various commandline arguments as advertised
- print version
- disable hardware optimization
- set client-name
- prevent port-connections
* Use JACK -- previously hardour only worked if
Ardour was compiled with JACK as *only* backend.
Other backends are listed before JACK, set_default_backend()
never picks JACK unless it's the only one.
Other backends need configuration, or EngineState from config.
This is currently handled in the GUI's engine-dialog..
