Fix #11738: Use an ASCII compatible session key

Commit 1416aaf deprecated
$g_session_key in favour of a unique key automatically derived from
$g_crypto_master_salt. However a bug existed in this commit whereby the
output of the hash() function was raw data, thus leading to failure of
PHP sessions. We need to ensure that the session key is ASCII
compatible.

core/session_api.php

@@ -102,7 +102,7 @@ function __construct( $p_session_id=null ) {
 		global $g_cookie_secure_flag_enabled;
 		global $g_cookie_httponly_flag_enabled;
 
-		$this->key = hash( 'whirlpool', 'session_key' . config_get_global( 'crypto_master_salt' ), true );
+		$this->key = hash( 'whirlpool', 'session_key' . config_get_global( 'crypto_master_salt' ), false );
 
 		# Save session information where specified or with PHP's default
 		$t_session_save_path = config_get_global( 'session_save_path' );