Fix failing tests due to symfony/yaml autoloading

- phpunit/phpunit was relying on functionality from symfony/yaml that was
  removed in version 2.2.0; pinning symfony/yaml to 2.1.* solves those issues.
Merge branch 'hotfix/yaml-dev-version'

Fixes for symfony/yaml autoloading
Reworked polyfill support for Zend\Stdlib\ArrayObject

- Instead of using an autoload file, instead created two separate classes, named
  after the type of support they provide. The file Zend\Stdlib\ArrayObject now
  simply has a conditional in it; based on the condition met, a class_alias() is
  created -- and from then on, that alias will be used for
  Zend\Stdlib\ArrayObject.

- Removed autoload.files entries from composer.json files; no longer necessary.

- One test failure currently in doing a comparison of merged array objects; will
  investigate in a later commit.
Reworked polyfill support for Zend\Session

- Created Zend\Session\Container and Zend\Session\Storage\SessionArrayStorage
  namespaces. Each contains PhpLegacyCompatibility and PhpReferenceCompatibility
  classes. The classes with the same name as the new namespaces each use
  conditionals to execute class_alias() commands in order to perform
  version-specific polyfills.
- Removed compatibility/autoload.php from composer.json autoload.files; no
  longer necessary.
- All tests are running!
Solved failing test in ArrayObject tests

- changed a typehint from "ArrayObject" to "self"
Fix failing Zend\Session test under 5.3.3

- bad import
Re-added autoload.php files

- BC measure, so that code referencing these files doesn't break
Fix typo

- per @DASPRiD
Fix polyfill support issue in CSRF validator

- typehint on AbstractContainer
- when instantiating a Container instance, use fully qualified class name in
  order to trigger alias