Add: set @vars for build, previous build etc. for later comparison
Add: compare status of last build (if available) to current build
Add: only deliver when statuses differ, or when we're sending at every build
Add: checkbox to email notification settings page
Fix: use a more explicit checkbox value
Fix: use the method rather than the attribute (easier to test)
Add: test of success>success>failure builds
Fix: label to match up with form element
Up: refactor decision into if it's changed, or we don't care
Up: delay fetching previous build, and replace iteration with Project.previous_build_id
Merge pull request #255 from seawolfsanctuary/feature/selective_email_notify

E-mail only when build status has changed