Avoid redirecting then rendering in private Concerto, close #836.
Check the remote version as robustly as github version.

The OpenURI-based remote version fetching was passing a :read_timeout option which doesn't exist in Ruby 1.8.7, causing it to error out and return nil.  As a result, 1.8.7 users were alway hitting the github-based fetching and potentially hitting limits there.