ui.backend.gtk: add surrounding signal handler for input methods
ui.backend.gtk: add surrounding signal handler for input methods

untested, as i don't think my IM is using this feature

bjourne/factor,bjourne/factor,bpollack/factor,factor/factor,dch/factor,sarvex/factor-lang,slavapestov/factor,factor/factor,bpollack/factor,AlexIljin/factor,tgunr/factor,sarvex/factor-lang,dch/factor,nicolas-p/factor,bjourne/factor,nicolas-p/factor,slavapestov/factor,tgunr/factor,dch/factor,nicolas-p/factor,sarvex/factor-lang,AlexIljin/factor,bjourne/factor,factor/factor,factor/factor,AlexIljin/factor,factor/factor,slavapestov/factor,AlexIljin/factor,AlexIljin/factor,sarvex/factor-lang,nicolas-p/factor,slavapestov/factor,mrjbq7/factor,nicolas-p/factor,AlexIljin/factor,tgunr/factor,sarvex/factor-lang,dch/factor,slavapestov/factor,tgunr/factor,bpollack/factor,bpollack/factor,nicolas-p/factor,bpollack/factor,sarvex/factor-lang,AlexIljin/factor,bjourne/factor,mrjbq7/factor,mrjbq7/factor,tgunr/factor,sarvex/factor-lang,bjourne/factor,slavapestov/factor,bpollack/factor,slavapestov/factor,mrjbq7/factor,dch/factor,tgunr/factor,bjourne/factor,dch/factor,factor/factor,mrjbq7/factor,nicolas-p/factor,mrjbq7/factor,bpollack/factor