rob-bugson sγur Will Kahn-Greene

Does the following:

• adds Bugzilla links to GitHub pull request page to bugs listed in the pull request summary
• adds Bugzilla links to GitHub compare pages to bugs listed in commits
• adds "Attach to bug" link to GitHub pull request page to bugs listed in pull request summary
• if the pull request has been merged, adds a "Add merge comment" link to create a comment on bugs listed in the pull request summary with relevant details about the merge

This automates several things people who use GitHub for their project, but use Bugzilla for tracking issues.