ensures compiled /source/stylesheets/screen.css exists before running watch and preview tasks, fixes #214

Rakefile

@@ -58,6 +58,7 @@ desc "Watch the site and regenerate when it changes"
 task :watch do
   raise "### You haven't set anything up yet. First run `rake install` to set up an Octopress theme." unless File.directory?(source_dir)
   puts "Starting to watch source with Jekyll and Compass."
+  system "compass compile --css-dir #{source_dir}/stylesheets" unless File.exist?("#{source_dir}/stylesheets/screen.css")
   jekyllPid = Process.spawn("jekyll --auto")
   compassPid = Process.spawn("compass watch")
 
@@ -73,6 +74,7 @@ desc "preview the site in a web browser"
 task :preview do
   raise "### You haven't set anything up yet. First run `rake install` to set up an Octopress theme." unless File.directory?(source_dir)
   puts "Starting to watch source with Jekyll and Compass. Starting Rack on port #{server_port}"
+  system "compass compile --css-dir #{source_dir}/stylesheets" unless File.exist?("#{source_dir}/stylesheets/screen.css")
   jekyllPid = Process.spawn("jekyll --auto")
   compassPid = Process.spawn("compass watch")
   rackupPid = Process.spawn("rackup --port #{server_port}")