[ticket/14269] Use http_exceptions in the installer instead of die()

PHPBB3-14269

phpBB/language/en/install.php

@@ -82,6 +82,9 @@ $lang = array_merge($lang, array(
 	<p>Only those databases supported on your server will be displayed.',
 
 	'ACP_LINK'	=> 'Take me to <a href="%1$s">the ACP</a>',
+
+	'INSTALL_PHPBB_IS_ALREADY_INSTALLED'	=> 'phpBB is already installed.',
+	'INSTALL_PHPBB_IS_NOT_INSTALLED'		=> 'phpBB is not installed yet.'
 ));
 
 // Requirements translation