build: Bump vte dep
screen: Change arbitraty constant

Doesn't matter which number we use, but don't use a nonobious choice.
screen: Only show right-click menu when the application hasn't handled the event itself

vte now sends the event to the terminal application (in mouse tracking mode). In that
case, don't pop up the gnome-terminal popup menu.

https://bugzilla.gnome.org/show_bug.cgi?id=13299
screen: Simplify code by using cleanup attribute