$var is valid unix timestamp
<p>I need a function to validate if the content of a variable is a valid unix timestamp.</p>

<p>I've checked this thread: <a href="http://stackoverflow.com/questions/2524680/check-whether-the-string-is-a-unix-timestamp">Check whether the string is a unix timestamp</a> but the problem is that the function in the most voted answer still can cause some errors, for eg:</p>

<pre><code>function is_timestamp($timestamp)
{
   return ((string) (int) $timestamp === $timestamp)
   &amp;&amp; ($timestamp &lt;= PHP_INT_MAX)
   &amp;&amp; ($timestamp &gt;= ~PHP_INT_MAX);
}

// Some tests:
$timestamp = 1289216307;
var_dump(is_timestamp($timestamp));
var_dump(date('Y-m-d', $timestamp));

// result
bool(false)
string(10) "2010-11-08" 

$timestamp = '20101108';
var_dump(is_timestamp($timestamp));
var_dump(date('Y-m-d', $timestamp));

// result
bool(true)
string(10) "1970-08-21" 
</code></pre>

<p>Here, the first should be <strong>TRUE</strong> and the second should be <strong>FALSE</strong> so, what's the best way to test if a $var is a real valid unix timestamp?</p>
