Make exception message when setting secure PHP session cookies through an...

Make exception message when setting secure PHP session cookies through an insecure channel coincident with the message in SimpleSAML\Utils\HTTP::setCookie().

lib/SimpleSAML/SessionHandlerPHP.php

@@ -323,7 +323,7 @@ class SimpleSAML_SessionHandlerPHP extends SimpleSAML_SessionHandler
 
         if ($cookieParams['secure'] && !\SimpleSAML\Utils\HTTP::isHTTPS()) {
             throw new \SimpleSAML\Error\CannotSetCookie(
-                'Secure cookies not allowed on http.',
+                'Setting secure cookie on plain HTTP is not allowed.',
                 \SimpleSAML\Error\CannotSetCookie::SECURE_COOKIE
             );
         }