Extend Hashes with + operator

I ran into a case where I needed to merge an array of hashes and was
disappointed that I couldn't use ActiveSupport's Enumerable#sum
extension solely for want of Hash#+ ... so I added it as an alias to
Hash#merge for fun.

Given:

  a = {:a => 1, :b => 2}
  b = {:b => 3, :c => 4}
  c = {:a => 2, :d => 5}

  d = [a, b, c]

... what was previously written:

  a.merge(b)
  d.inject {|sum, h| sum.merge(h)}

... can now be written:

  a + b
  d.sum #=> {:a => 2, :b => 3, :c => 4, :d => 5}

My favorite usage, though, reads something like:

  def create_foo_with_defaults(options = {})
    defaults = {...}
    Foo.create!(defaults + options)
  end

Ticket and patch (vs. r8062, with tests): http://dev.rubyonrails.org/ticket/10047

Please review and comment/+1.

Thanks!

--j