ActiveSupport::OrderedHash#update Does Not Set Keys

Hi all,

On versions of Ruby prior to 1.9, using update on an
ActiveSupport::OrderedHash will not set the keys correctly. This means
that it is not possible to iterate over the hash using each or get the
array of keys.

For example:

    hash = ActiveSupport::OrderedHash.new
    hash.update(:name => "Bob")
    # => #<OrderedHash {:name=>"Bob"}>
    hash.keys
    # => []
    hash.each do |key, value|
      puts value
    end
    # => []

This can be resolved by simply aliasing update to merge! as per
Rubinius' implementation (c.f. http://github.com/evanphx/rubinius/blob/master/kernel/common/hash.rb#L447
).

I have posted a patch including tests at
https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/4973-patch-activesupportorderedhashupdate-does-not-set-keys
and would appreciate any feedback whatsoever.