Replace method to get all application railties

Rails 4 API has changed and now we need to do:

  application.railties._all

Instead of just:

  application.railties._all

Otherwise it throws:

  undefined method `all' for #<Rails::Engine::Railties:0xa25b9e4> (NoMethodError)
Remove AS `encoding_aware` reference

It was removed in Rails 4. See https://github.com/rails/rails/pull/4160
for details.
Allow Rails backwards compatibility

Add some tweaks to make it possible to run the specs and the gem itself
on both Rails 4 and 3 versions

Users should be able to bundle using a specific Rails version by
specifying the RAILS env var
Run specs against ruby 1.9.3 and 2.0.0 on travis ci
Update deface dependency to 1.6.0

Related to:
spree/spree#2751
spree/spree#2650
spree/spree#2633
Merge branch 'rails4-working' of github.com:huoxito/deface into huoxito-rails4-working

Conflicts:
	.travis.yml
	Gemfile
	deface.gemspec
	spec/spec_helper.rb
rc3