Merge branch '3.0'

diff --cc wcfsetup/install/files/lib/system/WCF.class.php
index c9c167b611aa57a97f4e64af51258604d423c23e,e998fdb4993764e4f93d8890f0699f07e2e44b32..0c129ac3608d0ef2759a46e4706698385519e4ca
--- 1/wcfsetup/install/files/lib/system/WCF.class.php
--- 2/wcfsetup/install/files/lib/system/WCF.class.php
+++ b/wcfsetup/install/files/lib/system/WCF.class.php
@@@ -284,9 -273,9 +284,9 @@@ class WCF 
                        // Especially the `identity` value appears to be unrecognized by some of them, hence
                        // we'll just gzip the output of the exception to prevent them from tampering.
                        // This part is copied from `HeaderUtil` in order to isolate the exception handler!
-                       if (HTTP_ENABLE_GZIP && !defined('HTTP_DISABLE_GZIP')) {
+                       if (defined('HTTP_ENABLE_GZIP') && HTTP_ENABLE_GZIP && !defined('HTTP_DISABLE_GZIP')) {
 -                              if (function_exists('gzcompress') && !@ini_get('zlib.output_compression') && !@ini_get('output_handler') && isset($_SERVER['HTTP_ACCEPT_ENCODING']) && strstr($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip')) {
 -                                      if (strstr($_SERVER['HTTP_ACCEPT_ENCODING'], 'x-gzip')) {
 +                              if (function_exists('gzcompress') && !@ini_get('zlib.output_compression') && !@ini_get('output_handler') && isset($_SERVER['HTTP_ACCEPT_ENCODING']) && strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== false) {
 +                                      if (strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'x-gzip') !== false) {
                                                @header('Content-Encoding: x-gzip');
                                        }
                                        else {