sometimes, you just have to do what a windows programmer would do. add a global signa...

sometimes, you just have to do what a windows programmer would do. add a global signal, ARDOUR::GUIIdle() which can be used in the middle of long-running backend operations to give the GUI a chance to update. use it while adding routes.

git-svn-id: svn://localhost/ardour2/branches/3.0@13650 d708f5d6-7413-0410-9779-e7cbd77b26cf