Disable incremental regeneration by default in Jekyll 3.0

Disable the feature as it's still not 100% working 100% of the time. Feature
can be re-enabled by specifying `full_rebuild: false` in the configuration

lib/jekyll/configuration.rb

@@ -22,7 +22,7 @@ module Jekyll
       'keep_files'    => ['.git','.svn'],
       'encoding'      => 'utf-8',
       'markdown_ext'  => 'markdown,mkdown,mkdn,mkd,md',
-      'full_rebuild'  => false,
+      'full_rebuild'  => true,
 
       # Filtering Content
       'show_drafts'   => nil,

test/test_regenerator.rb

@@ -130,7 +130,8 @@ class TestRegenerator < JekyllUnitTest
 
       @site = Site.new(Jekyll.configuration({
         "source" => source_dir,
-        "destination" => dest_dir
+        "destination" => dest_dir,
+        "full_rebuild" => false
       }))
 
       @site.process