inch-like progress on defining the API for AudioBackend and separating AudioEngine from this
changes to audioengine.h
pre-initial version of AudioBackend API (still under heavy development)
more miscellaneous changes for audioengine, all of this is still far from actually compiling
part-way through getting the audioengine changes to compile
new file
most of libardour now actually compiles
start work on JACK specific audiobackend and port engine
small steps toward getting this all working - add new JackConnection object to share jack_client_t between AudioBackend and PortEngine
jack_audiobackend.cc finally compiles
remove compile errors (still will not link and JACKPortEngine is not close to done)
more stuff compiles
even more stuff compiles
full compilation and linking (coding not finished, will not run)
start code reorganization needed to deal with backend choices. compiles, links and runs as far as the startup screen now
audioengine branch can now load and run at least one test session.

currently hard-coded to deal only with the situation where JACK is already running
advance track's play-position even if processing is locked

fixes
  * http://tracker.ardour.org/view.php?id=5628
  * http://tracker.ardour.org/view.php?id=5561
add tim's jack_utils code to rationalize setup of JACK config
add file
fix problem with session exit caused by dangling unused members in AudioEngine