Allow setting protoc source as an environment variable when compiling
Allow setting protoc source as an environment variable when compiling

ruby-protobuf/protobuf,ruby-protobuf/protobuf,film42/protobuf,lookout/protobuffy,quixoten/protobuf,film42/protobuf,zanker/protobuf,brianstien/protobuf,zanker/protobuf,quixoten/protobuf,localshred/protobuf,localshred/protobuf,brianstien/protobuf,lookout/protobuffy