Made it possible to enter categories from YAML as an array.

lib/jekyll/post.rb

@@ -49,7 +49,13 @@ module Jekyll
         if self.data.has_key?('category')
           self.categories << self.data['category']
         elsif self.data.has_key?('categories')
-          self.categories = self.data['categories'].split
+          # Look for categories in the YAML-header, either specified as
+          # an array or a string.
+          if self.data['categories'].kind_of? String
+            self.categories = self.data['categories'].split
+          else
+            self.categories = self.data['categories']
+          end
         end
       end
     end

test/source/_posts/2009-01-27-array-categories.textile

@@ -0,0 +1,10 @@
+---
+layout: default
+title: Array categories in YAML
+categories:
+- foo
+- bar
+- baz
+---
+
+Best *post* ever

test/test_post.rb

@@ -87,10 +87,16 @@ class TestPost < Test::Unit::TestCase
   end
 
   def test_yaml_categories
-    p = Post.new(File.join(File.dirname(__FILE__), *%w[source]), '',  "2009-01-27-categories.textile")
-    assert p.categories.include?('foo')
-    assert p.categories.include?('bar')
-    assert p.categories.include?('baz')
+    p1 = Post.new(File.join(File.dirname(__FILE__), *%w[source]), '',
+                  "2009-01-27-categories.textile")
+    p2 = Post.new(File.join(File.dirname(__FILE__), *%w[source]), '',
+                  "2009-01-27-array-categories.textile")
+    
+    [p1, p2].each do |p|
+      assert p.categories.include?('foo')
+      assert p.categories.include?('bar')
+      assert p.categories.include?('baz')
+    end
   end
   
   def test_render