SX cap production setup files

lib/capistrano/tasks/check_revision.cap

@@ -0,0 +1,14 @@
+namespace :deploy do
+  desc "checks whether the currently checkout out revision matches the
+        remote one we're trying to deploy from"
+  task :check_revision do
+    branch = fetch(:branch)
+    unless `git rev-parse HEAD` == `git rev-parse #{branch}`
+      puts "WARNING: HEAD is not the same as #{branch}"
+      puts "Run `git push` to sync changes or make sure you've"
+      puts "checked out the branch: #{branch} as you can only deploy"
+      puts "if you've got the target branch checked out"
+      exit
+    end
+  end
+end