Glib::thread_init has been deprecated since 2.32,ib
is no longer necessary and no longer has any effect.
This fixes builds with modern glib[mm] versions, notably
with msys2 in Windows.
Export now happens directly to file (unless normalizing is required), and can be easily optimized even further.
The Session process connection is still broken during export (as it was before this commit also).
git-svn-id: svn://localhost/ardour2/branches/3.0@6401 d708f5d6-7413-0410-9779-e7cbd77b26cf
