Toss up an abort message if Manifest.txt doesn't already exist in the

rails app. Long term, we should probably help the user out with
generating it but for these alpha versions, this should be okay.

lib/harker/gemify.rb

@@ -28,7 +28,11 @@ def self.gemify(rails_root)
 
     lib = "# Allow rubygems to load this app
 require File.dirname(__FILE__) + '/../config/environment'"
-
+
+    unless File.exist?(rails_root + '/Manifest.txt')
+      abort "Create a Manifest.txt with a list of the files from your Rails app that you'd like to package"
+    end
+
     File.open(rails_root + '/Rakefile', 'a') { |fp| fp.puts hoe }
     puts "Added hoe block to Rakefile."
     FileUtils.mkdir_p(rails_root + '/bin')