Replace SHAs with links in commit messages.

This helps out a bit with the commit/comment linking problem. You can write a
commit message like "Fixes isses from ef220ba66954e705fa7c8f26ad8f81db23e423d5"
for a fixup commit and then the message will have a link to the original.

models/commit.rb

@@ -44,5 +44,6 @@ def format_message
            .newlines_to_html
            .link_github_issue("ooyala", git_repo.name)
            .link_jira_issue
+           .replace_shas_with_links(git_repo.name)
   end
 end