[Process] fixed HHVM usage on the CLI
upgraded PHPUnit to version 4 for better HHVM support
fixed float comparison in unit tests for HHVM
bug #10579 HHVM fixes (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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HHVM fixes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Fixes support for HHVM in the Process component and upgraded PHPUnit to version 4 for the same reason.

Commits
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9e6af95 fixed float comparison in unit tests for HHVM
73189b1 upgraded PHPUnit to version 4 for better HHVM support
8fbea0f [Process] fixed HHVM usage on the CLI