rjs-build should throw error compilation fail

[nabana]

Please alter the rjs-build task to transclude the error message from r.js if build fails. That is a big build step and would be important to know if it passes. It also includes sources from webgme and domain tools repositories and it would be a good indication of not having the most up-to-date versions installed. (like it happened to me today)

Current format:

    exec('node ./node_modules/requirejs/bin/r.js -o ./utils/build/webcyphy.plugins/cbuild.js', function () {
        console.log('Done requireJS build!');
    });

[pmeijer]

I've fixed the error propagation, however I'm not sure if it's feasible to guarantee the latest webgme/-domain-tools. The are not required by version (currently) and to pull the master branches each build would be painfully slow. I'm open for suggestions here though..