[2.0] [Form] [Locale] PHP 5.5 compatibility fixes

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: unknown, can't run the test suite on 2.0 due to `Doctrine\DBAL\Logging\DebugStack` not being found
Fixes the following tickets: N/A
Todo: None
License of the code: MIT
Documentation PR: N/A

A backport of #6647 to the Symfony 2.0 branch, as requested. This affects a couple of files that aren't affected on 2.1.