Some way to specify which version of Jekyll to use

[pathawks]

Now that we are including a Gemfile in the output site, it would be nice to specify the version of Jekyll to use for building the site. This way, we could test against (ie:) pull request branches as well as the master branch.

Perhaps we could check for some environment variable and, if it is non-null, use that in Gemfile instead of the gem "jekyll" line?

[DirtyF]

gem "jekyll", "#{ENV["JEKYLL_VERSION"]}" if ENV["JEKYLL_VERSION"]?

[pathawks]

It will have to be more flexible than that, because maybe I want something like

gem 'jekyll', :github => 'jekyll/jekyll', :branch => 'related-posts-perf-improvements'

Or maybe I want a specific commit. Or maybe I want it pulled from my repo instead of jekyll/jekyll