Improvements to hosting with Github Pages:

1. Push deployment task pulls first, avoiding a --force push
  2. Improvements to rake task setup_github_pages:
    - Now only rewrites _config.yml if in default state
    - Attempts a pull from deploy repo before setting up as a new project
    - Detects conflicts between CNAME and _config.yml url
    - Links to GitHub's help documentation for CNAME setup
Fixes #561

Rakefile

@@ -221,7 +221,6 @@ task :deploy do
     File.delete(".preview-mode")
     Rake::Task[:generate].execute
   end
-
   Rake::Task[:copydot].invoke(source_dir, public_dir)
   Rake::Task["#{deploy_default}"].execute
 end
@@ -249,21 +248,29 @@ end
 
 desc "deploy public directory to github pages"
 multitask :push do
+  if File.directory?(deploy_dir)
     puts "## Deploying branch to Github Pages "
     (Dir["#{deploy_dir}/*"]).each { |f| rm_rf(f) }
     Rake::Task[:copydot].invoke(public_dir, deploy_dir)
+    puts "Attempting pull, to sync local deployment repository"
+    cd "#{deploy_dir}" do
+      system "git pull origin #{deploy_branch}"
+    end
     puts "\n## copying #{public_dir} to #{deploy_dir}"
     cp_r "#{public_dir}/.", deploy_dir
     cd "#{deploy_dir}" do
       system "git add ."
       system "git add -u"
-    puts "\n## Commiting: Site updated at #{Time.now.utc}"
       message = "Site updated at #{Time.now.utc}"
+      puts "\n## Commiting: #{message}"
       system "git commit -m \"#{message}\""
       puts "\n## Pushing generated #{deploy_dir} website"
-    system "git push origin #{deploy_branch} --force"
+      system "git push origin #{deploy_branch}"
       puts "\n## Github Pages deploy complete"
     end
+  else
+    puts "This project isn't configured for deploying to Github Pages\nPlease run `rake setup_github_pages[your-deployment-repo-url]`." 
+  end
 end
 
 desc "Update configurations to support publishing to root or sub directory"
@@ -311,6 +318,8 @@ task :setup_github_pages, :repo do |t, args|
   user = repo_url.match(/:([^\/]+)/)[1]
   branch = (repo_url.match(/\/[\w-]+.github.com/).nil?) ? 'gh-pages' : 'master'
   project = (branch == 'gh-pages') ? repo_url.match(/\/([^\.]+)/)[1] : ''
+  url = "http://#{user}.github.com"
+  url += "/#{project}" unless project == ''
   unless `git remote -v`.match(/origin.+?octopress.git/).nil?
     # If octopress is still the origin remote (from cloning) rename it to octopress
     system "git remote rename origin octopress"
@@ -325,34 +334,65 @@ task :setup_github_pages, :repo do |t, args|
       puts "Master branch renamed to 'source' for committing your blog source files"
     else
       unless !public_dir.match("#{project}").nil?
-        system "rake set_root_dir[#{project}]"
+        Rake::Task[:set_root_dir].invoke(project)
       end
     end
   end
-  url = "http://#{user}.github.com"
+
-  url += "/#{project}" unless project == ''
+  # Configure deployment repository
-  jekyll_config = IO.read('_config.yml')
-  jekyll_config.sub!(/^url:.*$/, "url: #{url}")
-  File.open('_config.yml', 'w') do |f|
-    f.write jekyll_config
-  end
   rm_rf deploy_dir
   mkdir deploy_dir
   cd "#{deploy_dir}" do
     system "git init"
+    system "git remote add origin #{repo_url}"
+    puts   "Attempting to pull from repository"
+    system "git pull origin #{branch}"
+    unless File.exist?('index.html')
       system "echo 'My Octopress Page is coming soon …' > index.html"
       system "git add ."
       system "git commit -m \"Octopress init\""
       system "git branch -m gh-pages" unless branch == 'master'
-    system "git remote add origin #{repo_url}"
+    end
+  end
+
+  # Configure deployment setup in Rakefile
   rakefile = IO.read(__FILE__)
   rakefile.sub!(/deploy_branch(\s*)=(\s*)(["'])[\w-]*["']/, "deploy_branch\\1=\\2\\3#{branch}\\3")
   rakefile.sub!(/deploy_default(\s*)=(\s*)(["'])[\w-]*["']/, "deploy_default\\1=\\2\\3push\\3")
   File.open(__FILE__, 'w') do |f|
     f.write rakefile
   end
+
+  # Configure published url 
+  jekyll_config = IO.read('_config.yml')
+  current_url = /^url:\s?(.*$)/.match(jekyll_config)[1]
+  has_cname = File.exists?("#{source_dir}/CNAME")
+  if current_url == 'http://yoursite.com'
+    jekyll_config.sub!(/^url:.*$/, "url: #{url}") 
+    File.open('_config.yml', 'w') do |f|
+      f.write jekyll_config
     end
-  puts "\n---\n## Now you can deploy to #{url} with `rake deploy` ##"
+    current_url = url
+  end
+
+  puts "\n========================================================"
+  if has_cname
+    cname = IO.read("#{source_dir}/CNAME").chomp
+    current_short_url = /\/{2}(.*$)/.match(current_url)[1]
+    if cname != current_short_url
+      puts "!! WARNING: Your CNAME points to #{cname} but your _config.yml url is set to #{current_short_url} !!"
+      puts "For help with setting up a CNAME follow the guide at http://help.github.com/pages/#custom_domains"
+    else
+      puts "Github Pages will host your site at http://#{cname}"
+    end
+  else
+    puts "Github Pages will host your site at #{url}."
+    puts "To host at \"your-site.com\", configure a CNAME: `echo \"your-domain.com\" > #{source_dir}/CNAME`"
+    puts "Then change the url in _config.yml from #{current_url} to http://your-domain.com"
+    puts "Finally, follow the guide at http://help.github.com/pages/#custom_domains for help pointing your domain to Github Pages"
+  end
+  puts "Deploy to #{repo_url} with `rake deploy`"
+  puts "========================================================"
 end
 
 def ok_failed(condition)