Add additional specs for support for Rails' HWIA

* Rails, in the ActiveSupport module ships with it's own version of
  indifferent access hash that tries to alias methods in a similar way
  to that of the Hashie's version of Indifferent Access. This causes
  the stack to overflow when a Rails' param object is directly passed in
  as an argument to a class that is extended with the Indifferent access
  functionality by Hashie::Extensions::IndifferentAccess

  For example:

	require 'active_support/hash_with_indifferent_access'
	require 'hashie'
	require 'pry'

	class A < Hash
	  include Hashie::Extensions::Coercion
	  include Hashie::Extensions::MergeInitializer
	  include Hashie::Extensions::Dash::IndifferentAccess
	end

	two_dimensional_hash = {
	  'a' =>  '1',
	  'b' =>  '2',
	  'c'=>  {
	    'd'=>  '3',
	    'e'=> '4'
	  }
	}

	indifferent_hash = ActiveSupport::HashWithIndifferentAccess.new two_dimensional_hash

	A.new(indifferent_hash)

  This would result in a stack error:

	hashie/extensions/merge_initializer.rb:20:in `initialize'
	hashie/lib/hashie/extensions/merge_initializer.rb:20:in `each'
	hashie/lib/hashie/extensions/merge_initializer.rb:21:in `block in
	initialize'
	hashie/lib/hashie/extensions/indifferent_access.rb:103:in
	`indifferent_writer'
	hashie/lib/hashie/extensions/indifferent_access.rb:82:in
	`convert_value'
	hashie/lib/hashie/extensions/indifferent_access.rb:63:in `inject'
	hashie/lib/hashie/extensions/indifferent_access.rb:57:in `inject!'
	hashie/lib/hashie/extensions/indifferent_access.rb:74:in `convert!'
	hashie/lib/hashie/extensions/indifferent_access.rb:74:in `each'
	hashie/lib/hashie/extensions/indifferent_access.rb:75:in `block in
	convert!'
	hashie/vendor/ruby/2.1.0/gems/activesupport-3.0.20/lib/active_support/hash_with_indifferent_access.rb:45:in
	`[]='
  < above line repeats until a stack error >
Merge pull request #2 from kgrz/add-additional-specs-in-indifferent-access

Add additional specs in indifferent access