Auto-enable watch on 'serve'.

Addresses @kneath's and @chibicode's comments in #2695.

Rakefile

@@ -146,7 +146,7 @@ namespace :site do
     # Generate the site in server mode.
     puts "Running Jekyll..."
     Dir.chdir("site") do
-      sh "#{File.expand_path('bin/jekyll', File.dirname(__FILE__))} serve --watch"
+      sh "#{File.expand_path('bin/jekyll', File.dirname(__FILE__))} serve"
     end
   end
 

lib/jekyll/command.rb

@@ -51,7 +51,7 @@ module Jekyll
         c.option 'config',  '--config CONFIG_FILE[,CONFIG_FILE2,...]', Array, 'Custom configuration file'
         c.option 'future',  '--future', 'Publishes posts with a future date'
         c.option 'limit_posts', '--limit_posts MAX_POSTS', Integer, 'Limits the number of posts to parse and publish'
-        c.option 'watch',   '-w', '--watch', 'Watch for changes and rebuild'
+        c.option 'watch',   '-w', '--[no-]watch', 'Watch for changes and rebuild'
         c.option 'force_polling', '--force_polling', 'Force watch to use polling'
         c.option 'lsi',     '--lsi', 'Use LSI for improved related posts'
         c.option 'show_drafts',  '-D', '--drafts', 'Render posts in the _drafts folder'

lib/jekyll/commands/serve.rb

@@ -20,7 +20,8 @@ module Jekyll
             c.option 'skip_initial_build', '--skip-initial-build', 'Skips the initial site build which occurs before the server is started.'
 
             c.action do |args, options|
-              options["serving"] ||= true
+              options["serving"] = true
+              options["watch"] = true unless options.key?("watch")
               Jekyll::Commands::Build.process(options)
               Jekyll::Commands::Serve.process(options)
             end

lib/jekyll/configuration.rb

@@ -211,7 +211,7 @@ module Jekyll
       if config.key?('auto') || config.key?('watch')
         Jekyll.logger.warn "Deprecation:", "Auto-regeneration can no longer" +
                             " be set from your configuration file(s). Use the"+
-                            " --watch/-w command-line option instead."
+                            " --[no-]watch/-w command-line option instead."
         config.delete('auto')
         config.delete('watch')
       end