Fix version_compare() calls for PHP 5.5.

Until PHP 5.5 hits beta, the version number for Git builds is still 5.5.0-dev,
which is less than 5.5.0alpha1 according to version_compare(). This means that
the branches for 5.5 aren't being executed on 5.5 snapshots at present.
merged branch LawnGnome/PHP-5.5-compat-2.0 (PR #6699)

This PR was merged into the 2.0 branch.

Commits
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c7bfce9 Fix version_compare() calls for PHP 5.5.

Discussion
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[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.