vim: use timeout instead of idle for constrain callback
vim: use timeout instead of idle for constrain callback

We tend to get in a accidental selection from mouse press/motion/release
when using the GIdleSource. Instead we can wait for a small timeout and
give ourselves more of a chance to avoid a visual mode transition.

GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview