Protobuf3 debuild

Uses docker and debian debuild to produce protobuf 3 packages for ubuntu/trusty.

A diff of all the changes made is available at changes.diff

Usage

To start the build, just run the following:

    $ make protobuf

The build is separated into 2 parts:

building the base build-image docker image, which does all the necessary setup, like install all dependent packages and tools,
building the protobuf package, which is just executing build.sh inside the build-image container.

This makes iterating on the packaging scripts faster, since the build-image is only built when its Dockerfile changes.