Fix commits table highlight
Add gitlab-shell/bin/check to rake gitlab:check

We sometimes encounter connectivity issues where gitlab-shell cannot
make API calls to the Rails application. There is a self-test script
`gitlab-shell/bin/check` that tries to connect to the API; this commit
runs that script as part of `rake gitlab:check`.
Merge branch 'gitlab-shell-check' of /home/git/repositories/gitlab/gitlabhq