Packagist is truncating `PackageLink` versions.

As a pseudo-code to reproduce the issue, try following:

```php
public function testDoesNotTruncateVersions()
{
    $version = str_repeat('>=1', 1000);
    $require = new \Packagist\WebBundle\Entity\RequireLink();

    $require->setPackageVersion($version);

    $this->entityManager->persist($require);
    $this->entityManager->flush($require);
    $this->entityManager->refresh($require);

    $this->assertSame($version, $require->getPackageVersion());
}
```
Merge pull request #464 from Ocramius/hotfix/constraint-truncation-hotfix

Packagist is truncating `PackageLink` versions.