Yield only one argument instead of splatting.

Add Changelog entry. Closes #4003

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Allow blocks for `count` with `ActiveRecord::Relation`, to work similar as
+    `Array#count`:
+
+        Person.where("age > 26").count { |person| gender == 'female' }
+
+    *Chris Finne & Carlos Antonio da Silva*
+
 *   Added support to `CollectionAssociation#delete` for passing `fixnum`
     or `string` values as record ids. This finds the records responding
     to the `id` and executes delete on them.

activerecord/lib/active_record/relation/calculations.rb

@@ -21,7 +21,7 @@ module Calculations
     #   # => queries people where "age > 26" then count the loaded results filtering by gender
     def count(column_name = nil, options = {})
       if block_given?
-        self.to_a.count { |*block_args| yield(*block_args) }
+        self.to_a.count { |item| yield item }
       else
         column_name, options = nil, column_name if column_name.is_a?(Hash)
         calculate(:count, column_name, options)
@@ -65,7 +65,7 @@ def maximum(column_name, options = {})
     #   # queries people where "age > 100" then perform a sum calculation with the block returns
     def sum(*args)
       if block_given?
-        self.to_a.sum(*args) { |*block_args| yield(*block_args) }
+        self.to_a.sum(*args) { |item| yield item }
       else
         calculate(:sum, *args)
       end