plugins: protect against faulty updates

Switching the tty causes the terminal to exit, which means
the package upgrade jobs are not done, leaving files in the
system that shouldn't be there.

The $search parameter is unused.

src/etc/inc/plugins.inc

@@ -30,9 +30,10 @@
  * scan plugins for legacy system
  * @return array
  */
-function plugins_scan($search = '')
+function plugins_scan()
 {
     $path = '/usr/local/etc/inc/plugins.inc.d/';
+    $clash = '/usr/local/etc/inc/';
     $ext = '.inc';
 
     $ret = array();
@@ -47,7 +48,8 @@ function plugins_scan($search = '')
     foreach ($plugins as $plugin) {
         $name = preg_replace('/' . preg_quote($path, '/') . '/', '', $plugin);
         $name = preg_replace('/' . preg_quote($ext, '/') . '/', '', $name);
-        if (!empty($search) && $search !== $name) {
+        /* if the old file still exists upgrade went wrong */
+        if (file_exists($clash . $name . $ext)) {
             continue;
         }
         $ret[$name] = $plugin;