Perform strict comparison for set() options array

[matthiasmullie]

The non-strict check results in false positives with a zero expiration time.
The following returns true for $nx, even though it's a valid options array & doesn't include nx.

$optionArrayOrExpiration = array(
    'xx', // if exists
    'ex' => 0 // expire time in seconds
);
$nx = in_array('nx', $optionArrayOrExpiration);

Making it a strict check fixes that:

$nx = in_array('nx', $optionArrayOrExpiration, true); // returns false

[facebook-github-bot]

This pull request has been imported into Phabricator, and discussion and review of the diff will take place at https://reviews.facebook.net/D33393

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