bug symfony#19827 [BrowserKit] Fix cookie expiration on 32 bit systems (jameshalsall)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes symfony#19827).

Discussion
----------

[BrowserKit] Fix cookie expiration on 32 bit systems

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#15739
| License       | MIT

On 32-bit systems the cookie expiration value was not being calculated
correctly as it was being fetched as an integer. When the timestamp exceeded
the PHP_INT_MAX size it would return an invalid value, breaking the cookie
construction.

The BrowserKit cookie has now been updated to get the timestamp as a string
which works around this platform limitation (similar to how it works in the Cookie
from HttpFoundation).

Commits
-------

68698f2 [BrowserKit] Fix cookie expiration on 32 bit systems

Author: fabpot

src/Symfony/Component/BrowserKit/Cookie.php

@@ -76,7 +76,7 @@ public function __construct($name, $value, $expires = null, $path = null, $domai
                 throw new \UnexpectedValueException(sprintf('The cookie expiration time "%s" is not valid.', $expires));
             }
 
-            $this->expires = $timestampAsDateTime->getTimestamp();
+            $this->expires = $timestampAsDateTime->format('U');
         }
     }
 
@@ -205,13 +205,13 @@ private static function parseDate($dateValue)
 
         foreach (self::$dateFormats as $dateFormat) {
             if (false !== $date = \DateTime::createFromFormat($dateFormat, $dateValue, new \DateTimeZone('GMT'))) {
-                return $date->getTimestamp();
+                return $date->format('U');
             }
         }
 
         // attempt a fallback for unusual formatting
         if (false !== $date = date_create($dateValue, new \DateTimeZone('GMT'))) {
-            return $date->getTimestamp();
+            return $date->format('U');
         }
 
         throw new \InvalidArgumentException(sprintf('Could not parse date "%s".', $dateValue));
@@ -304,6 +304,6 @@ public function isHttpOnly()
      */
     public function isExpired()
     {
-        return null !== $this->expires && 0 !== $this->expires && $this->expires < time();
+        return null !== $this->expires && 0 != $this->expires && $this->expires < time();
     }
 }