Always verify nix store on install
Always verify nix store on install

Just wasted a couple hours chasing shadows because the nix store got
corrupted and there was no indication of that anywhere.

Since an install is one-time only, might as well verify.  Optimization
showed that the copied files aren't read-only; fixed that as well.

Also, use /bin/sh since there's a good chance that this script will be
run on systems without /bin/bash

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