Added svn to vagrant.pp
Disabled god in vagrant.pp for now
Mentioning BuildAddonsTask in README
Optional limiting of updated addons

Mainly for easier debugging. Still needs to download all
packagist sources though, so speed gains are mainly in reduced
DB writes and PHP execution.
Include unreleased versions through branch alias
Fixed constraint parsing for SilverStripeVersion

Was comparing strings to objects, not sure how that ever worked :)