Sources now know about Session.
rearrange session directory heirarchy. remove tape_dir stuff.
NSD allows absolute/relative paths to be typed straight into the text entry.
Session history reloaded after all 3rd party registrations done.
Editor restores its ID; other objects still need this.
use g_mkdir_with_parents() instead of mkdir()
one example of using g_file_test() instead of access.
git-svn-id: svn://localhost/ardour2/trunk@908 d708f5d6-7413-0410-9779-e7cbd77b26cf