Switch to Go 1.5.1 (fixes #955)
Switch to Go 1.5.1 (fixes #955)

martindale/letsencrypt,thanatos/lets-encrypt-preview,stweil/letsencrypt,jsha/letsencrypt,twstrike/le_for_patching,kuba/letsencrypt,lbeltrame/letsencrypt,lbeltrame/letsencrypt,ghyde/letsencrypt,letsencrypt/letsencrypt,Sveder/letsencrypt,DavidGarciaCat/letsencrypt,DavidGarciaCat/letsencrypt,jsha/letsencrypt,VladimirTyrin/letsencrypt,kuba/letsencrypt,hsduk/lets-encrypt-preview,dietsche/letsencrypt,lmcro/letsencrypt,VladimirTyrin/letsencrypt,lmcro/letsencrypt,BillKeenan/lets-encrypt-preview,mrb/letsencrypt,twstrike/le_for_patching,sjerdo/letsencrypt,goofwear/letsencrypt,mrb/letsencrypt,mitnk/letsencrypt,thanatos/lets-encrypt-preview,goofwear/letsencrypt,Sveder/letsencrypt,ghyde/letsencrypt,dietsche/letsencrypt,hsduk/lets-encrypt-preview,BillKeenan/lets-encrypt-preview,wteiken/letsencrypt,piru/letsencrypt,letsencrypt/letsencrypt,brentdax/letsencrypt,jtl999/certbot,jtl999/certbot,bsmr-misc-forks/letsencrypt,xgin/letsencrypt,brentdax/letsencrypt,stweil/letsencrypt,bsmr-misc-forks/letsencrypt,martindale/letsencrypt,mitnk/letsencrypt,sjerdo/letsencrypt,wteiken/letsencrypt,xgin/letsencrypt,piru/letsencrypt,TheBoegl/letsencrypt,TheBoegl/letsencrypt