Merge remote-tracking branch 'refs/remotes/origin/2.1' into 3.0

diff --cc wcfsetup/install/files/lib/system/captcha/RecaptchaHandler.class.php
index 6d20889831cb8b61b3fe14a85ea99b7dfea6347e,8c3d111d99daf7ec4da4089d9446600cb677adb6..9f2a74157609913138402e0ed3c76536496b817b
--- 1/wcfsetup/install/files/lib/system/captcha/RecaptchaHandler.class.php
--- 2/wcfsetup/install/files/lib/system/captcha/RecaptchaHandler.class.php
+++ b/wcfsetup/install/files/lib/system/captcha/RecaptchaHandler.class.php
@@@ -46,9 -48,14 +46,14 @@@ class RecaptchaHandler implements ICapt
        }
        
        /**
 -       * @see \wcf\system\captcha\ICaptchaHandler::isAvailable()
 +       * @inheritDoc
         */
        public function isAvailable() {
+               if (!RECAPTCHA_PUBLICKEY || !RECAPTCHA_PRIVATEKEY) {
+                       // OEM keys are no longer supported, disable reCAPTCHA
+                       return false;
+               }
+               
                return true;
        }