Fix PHP 5.3.3 segmentation fault in unit tests

This PR fixes segmentation fault in unit tests with PHP 5.3.3, introduced in https://github.com/ezsystems/ezpublish-kernel/commit/047ce30136e6024126c6b5ef10fbd08b8a27fc18.
See [Travis](https://travis-ci.org/ezsystems/ezpublish-kernel/builds/6388186).

Additional fix: expectation for ```eztime``` FieldType::acceptValue() when timezone offset is negative.