keymap: Treat ALT as META
keymap: Treat ALT as META

https://bugzilla.gnome.org/show_bug.cgi?id=663779

thestinger/vte-ng,rvu95/vte,flaxandteal/gasket-vte,rvu95/vte,pjm0616/vte,rvu95/vte,thestinger/vte-ng,jessevdk/vte,thestinger/vte-ng,jessevdk/vte,asivokon/vte-fx,asivokon/vte-fx,flaxandteal/gasket-vte,saitoha/vte-sixel,asivokon/vte-fx,pjm0616/vte,rvu95/vte,saitoha/vte-sixel,flaxandteal/gasket-vte,saitoha/vte-sixel,jessevdk/vte,pjm0616/vte,jessevdk/vte,flaxandteal/gasket-vte,asivokon/vte-fx