[DSL] Changed, that global aggregation takes a block

Changed global aggregation to behave like a nested aggregation

Related: #213

Closes #228

lib/elasticsearch/dsl/search/aggregations/global.rb

@@ -16,7 +16,7 @@ module Aggregations
         # @see http://elasticsearch.org/guide/en/elasticsearch/reference/current/search-aggregations-bucket-global-aggregation.html
         #
         class Global
-          include BaseComponent
+          include BaseAggregationComponent
         end
 
       end

test/unit/aggregations/global_test.rb

@@ -12,7 +12,25 @@ class GlobalTest < ::Test::Unit::TestCase
           should "be converted to a Hash" do
             assert_equal({ global: {} }, subject.to_hash)
           end
-
+
+          should "take a block" do
+            subject = Global.new do
+            end
+            assert_equal({global: {} }, subject.to_hash)
+          end
+
+          should "define aggregations" do
+            subject = Global.new do
+              aggregation :foo do
+                terms field: "bar"
+              end
+            end
+            expected = {
+              aggregations: { foo: { terms: { field: "bar" } } },
+              global: {}
+            }
+            assert_equal(expected, subject.to_hash)
+          end
         end
       end
     end