Change log.Exit to log.Fatal, per latest Go release.
Change log.Exit to log.Fatal, per latest Go release.

R=nigeltao, r2
CC=golang-dev
http://codereview.appspot.com/4121055

csuideal/protobuf,trdata/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,ekle/protoc-gen-goweb,kung-foo/protobuf,alskjstl/protobuf,adnaan/protobuf,aoeu/protobuf,trdata/protobuf,ekle/protoc-gen-goweb_test,hailocab/protobuf,jeremyletang/protobuf,daemonl/protobuf,golang/protobuf,velocity-toolkit/protobuf-1,ArtemTeleshev/go-protobuf,mwitkow-io/protobuf,qinlodestar/protobuf,tamird/protobuf-2,jrbarron/protobuf,golang/protobuf,linkedin-inc/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,eduardiazf/protobuf,skyportsystems/go-protobuf,skyportsystems/go-protobuf,tamird/protobuf-2,jmptrader/protobuf-1,francoishill/protobuf