gmain: Mark some ref_count variables as volatile
gmain: Mark some ref_count variables as volatile

To make it more obvious they should exclusively be accessed with atomic
functions.

https://bugzilla.gnome.org/show_bug.cgi?id=737677

johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib