In case USE_KEY flag is active, RegexIterator->accept() should keep it's
old behavior which is to accept keys mapping arrays.
This broke after PHP 5.5 but was not noticed due to lack of tests for USE_KEY.
Three issues are addressed:
- RecursiveRegexIterator::accept() should accept non-empty arrays without
applying any regular expression and RegexIterator::accept() should not accept
an array.
- RegexIterator::accept() should not accept an atom that fails to match
anything, even when PREG_PATTERN_ORDER is used (which would return an array
of empty arrays).
- RecursiveRegexIterator::getChildren() should pass all constructor arguments
to its child iterator instead of just the regular expression.
