(ok 2.11.8) make safari set the actual timedate on dumps

patch to make safari set the actual timedate to the dump file :

in pma 2.11.7/export.php after line 365: header('Pragma: no-cache');
+ if ('SAFARI' == PMA_USR_BROWSER_AGENT) {
+ header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . ' GMT');
+ }

(thx Sebastian)
tested on safari/win2000 and mac-os (thx to ibenneth)