Old `script/bootstrap` & `script/build` were unfriendly to Go newbies
because they require the user having GOPATH set in their environment,
and either `godep` installed or `hg` to be able to fetch godep.

However, since dependencies are vendored, we don't have any real build
dependencies except Go itself.

- `script/bootstrap` now checks Go and installs Ruby test bundle
- `script/build` skips compiling if binary is up to date
- `script/test` runs both Go and Cucumber test suites

Advantages over scripts in `script/`:

- Works without gopath
- Works without godep

This only affects CI builds in cases when the bundle is not cached.

http://mislav.uniqpath.com/2013/12/travis-cached-bundle/

Hopefully speeds up builds

Works around travis-ci/travis-ci#1710

This silences passing notifications for new branches

References ba237b6b

Instruct it to fail on Ruby syntax warnings coming from only the code in
this project.

MRI 1.8.6 should be supported by hub, but it's not supported by Travis
anymore.