Added support DateTimeInterface (PHP 5.5) if available
feature #1234 Added support DateTimeInterface (PHP 5.5) if available (hidenorigoto)

This PR was squashed before being merged into the master branch (closes #1234).

Discussion
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Added support DateTimeInterface (PHP 5.5) if available

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | new BSD
| Doc PR        |

Commits
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ca61fac Added support DateTimeInterface (PHP 5.5) if available
updated CHANGELOG