edit/tty/tty.go: add function FlushInput
edit/tty/tty.go: add function FlushInput

elves/elvish,elves/elvish,beni55/elvish,elves/elvish,ke7ofi/elvish,elves/elvish,elves/elvish,CodyGuo/elvish,ke7ofi/elvish,beni55/elvish,CodyGuo/elvish