remove ardour_message.{cc,h}; JACK latency menu now shows correct settings at startup...

remove ardour_message.{cc,h}; JACK latency menu now shows correct settings at startup and changes are handled correctly; export range markers doesn't start with /path/to/export.wav, just /path/to; hopefully improve ruler scrolling a little; fixed up short_path() implementation ; fix for export unsetting JACK freewheel too soon ; use ISO 8061 timestamps for snapshot default names

git-svn-id: svn://localhost/ardour2/trunk@1400 d708f5d6-7413-0410-9779-e7cbd77b26cf