fix definition of RSS_BACKEND_TYPE (closes #99)

config.php-dist

@@ -9,7 +9,7 @@
 	define('DB_PASS', "XXXXXX");
 	//define('DB_PORT', '5432'); // when neeeded, PG-only
 
-	define(RSS_BACKEND_TYPE, "magpie");
+	define('RSS_BACKEND_TYPE', "magpie");
 	// magpie (stable) or simplepie (EXPERIMENTAL!)
 
 	define('MAGPIE_CACHE_DIR', '/var/tmp/magpie-ttrss-cache');