Harmonize PHPUnit version to 4.2 or above

Use the same version as the one on the dedicated "tests" page and link to phpunit.de
minor #4669 Harmonize PHPUnit version to 4.2 or above (xelaris)

This PR was merged into the 2.3 branch.

Discussion
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Harmonize PHPUnit version to 4.2 or above

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4547

Use the same version as the one on the dedicated "tests" page since #4552 and link to phpunit.de

Commits
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df25c36 Harmonize PHPUnit version to 4.2 or above