download-from-binary-cache.pl: Show if we're waiting for a URL
download-from-binary-cache.pl: Show if we're waiting for a URL

Previously, if a binary cache is hanging/unreachable/slow,
download-from-binary-cache.pl would also hang without any indication
to the user.  Now, if fetching a URL takes more than 5 seconds, it
will print a message to that effect.

gebner/nix,zimbatm/nix,joelmo/nix,gridaphobe/nix,ehmry/nix,bjornfor/nix,nbp/nix,dtzWill/nix,NixOS/nix,vizanto/nix,peti/nix,ehmry/nix,peti/nix,shlevy/nix,offlinehacker/nix,vizanto/nix,aucampia/nix,wmertens/nix,bennofs/nix,bjornfor/nix,vcunat/nix,rycee/nix,gebner/nix,tchajed/nix,NixOS/nix,puffnfresh/nix,layus/nix,ttuegel/nix,bjornfor/nix,rowhit/nix,rycee/nix,garbas/nix,pikajude/nix,peti/nix,nbp/nix,dtzWill/nix,jcumming/nix,tchajed/nix,gebner/nix,bennofs/nix,edolstra/nix,edolstra/nix,aucampia/nix,nbp/nix,wmertens/nix,rowhit/nix,edolstra/nix,acowley/nix,jcumming/nix,rowhit/nix,gridaphobe/nix,NixOS/nix,ysangkok/nix,vcunat/nix,edolstra/nix,tchajed/nix,bennofs/nix,puffnfresh/nix,zimbatm/nix,gridaphobe/nix,ttuegel/nix,offlinehacker/nix,shlevy/nix,garbas/nix,shlevy/nix,ysangkok/nix,rowhit/nix,nbp/nix,joelmo/nix,vcunat/nix,acowley/nix,ehmry/nix,dtzWill/nix,ehmry/nix,rycee/nix,pikajude/nix,gebner/nix,jcumming/nix,tchajed/nix,vizanto/nix,peti/nix,garbas/nix,dtzWill/nix,wmertens/nix,vizanto/nix,dezgeg/nix,NixOS/nix,shlevy/nix,bjornfor/nix,offlinehacker/nix,bennofs/nix,ttuegel/nix,dtzWill/nix,shlevy/nix,layus/nix,layus/nix,dezgeg/nix,rycee/nix,ysangkok/nix,puffnfresh/nix,dezgeg/nix,dezgeg/nix,ehmry/nix,garbas/nix,NixOS/nix,zimbatm/nix,ehmry/nix,pikajude/nix,joelmo/nix,zimbatm/nix,offlinehacker/nix,layus/nix,aucampia/nix,aucampia/nix,wmertens/nix,dezgeg/nix,acowley/nix,ttuegel/nix,puffnfresh/nix,jcumming/nix,peti/nix,edolstra/nix,acowley/nix,joelmo/nix,gridaphobe/nix,vcunat/nix,garbas/nix,rycee/nix,layus/nix