text: Don't accept new line characters in single line mode
text: Don't accept new line characters in single line mode

Modified Return key presses don't trigger ::activate so we would end
up adding an unprintable character to a single paragraph mode pango
layout which renders it as a box.

https://bugzilla.gnome.org/show_bug.cgi?id=623344

djdeath/clutter,Distrotech/clutter,djdeath/clutter-android,jigpu/clutter,heysion/clutter-clone,jigpu/clutter,heysion/clutter-clone,djdeath/clutter,ebassi/clutter,collects/clutter,GNOME/clutter,Distrotech/clutter,Distrotech/clutter,ebassi/clutter,ebassi/clutter,djdeath/clutter-android,collects/clutter,heysion/clutter-clone,GNOME/clutter,djdeath/clutter,Distrotech/clutter,djdeath/clutter-android,ebassi/clutter,jigpu/clutter,djdeath/clutter-android,collects/clutter,collects/clutter,djdeath/clutter-android,jigpu/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,GNOME/clutter,djdeath/clutter,djdeath/clutter,collects/clutter,jigpu/clutter,Distrotech/clutter,ebassi/clutter,heysion/clutter-clone,GNOME/clutter,djdeath/clutter,heysion/clutter-clone