Block syntax for update_attributes

ActiveRecord::Base#new and #create accepts both a Hash of attributes and a block:

  User.create(:first_name => 'Jamie') do |u|
    u.is_admin = false
  end

This patch adds that same functionality to update_attributes:

  user.update_attributes(:first_name => 'Jamie') do |u|
    u.is_admin = false
  end
  user.first_name #=> 'Jamie'
  user.is_admin   #=> false

A use case for this is in the administration area, where authenticated users might be allowed to update attributes that are otherwise protected.

Edited by Rohit Arondekar for formatting.