upgrade gitlab

  bump to gitlab 6-3-stage
  bump to gitlabshell 1.8.0
gitlab 6.4, init script is now managed by app

  Use /etc/default/gitlab \o/
install: add assets precompilation
fix missing gitlab init script
Merge pull request #105 from sbadia/upgrade/6-4

Bump puppet-gitlab (gitlab stable-6-4 and gitlab-shell 1.8.0)