nix repl: Fix multiline SIGINT handling.
nix repl: Fix multiline SIGINT handling.

Fixes #2076

peti/nix,dtzWill/nix,peti/nix,dtzWill/nix,zimbatm/nix,dtzWill/nix,dezgeg/nix,zimbatm/nix,rycee/nix,dezgeg/nix,dezgeg/nix,peti/nix,NixOS/nix,vcunat/nix,ehmry/nix,vcunat/nix,ehmry/nix,rycee/nix,layus/nix,layus/nix,shlevy/nix,shlevy/nix,layus/nix,dtzWill/nix,ehmry/nix,vcunat/nix,zimbatm/nix,NixOS/nix,shlevy/nix,layus/nix,shlevy/nix,ehmry/nix,rycee/nix,NixOS/nix,rycee/nix,rycee/nix,zimbatm/nix,pikajude/nix,layus/nix,NixOS/nix,NixOS/nix,pikajude/nix,pikajude/nix,vcunat/nix,peti/nix,shlevy/nix,dtzWill/nix,ehmry/nix,dezgeg/nix,peti/nix,dezgeg/nix,ehmry/nix