Close #141: build on gcc 5.1
Close #141: build on gcc 5.1

This required no more code changes (just had to compile a protobuf under
the same compiler and set -L and -rpath).

TigerZhang/logcabin,logcabin/logcabin,logcabin/logcabin,dankenigsberg/logcabin,gaoning777/logcabin,gaoning777/logcabin,chaozh/logcabin,tempbottle/logcabin,TigerZhang/logcabin,TigerZhang/logcabin,dankenigsberg/logcabin,TigerZhang/logcabin,logcabin/logcabin,gaoning777/logcabin,tempbottle/logcabin,chaozh/logcabin,logcabin/logcabin,chaozh/logcabin,dankenigsberg/logcabin,tempbottle/logcabin,gaoning777/logcabin,dankenigsberg/logcabin,tempbottle/logcabin,chaozh/logcabin