Issue #2794207 by alexpott: sys_get_temp_dir() can return a path with a trailing slash

core/includes/file.inc

@@ -1236,7 +1236,9 @@ function file_directory_os_temp() {
 
   foreach ($directories as $directory) {
     if (is_dir($directory) && is_writable($directory)) {
-      return $directory;
+      // Both sys_get_temp_dir() and ini_get('upload_tmp_dir') can return paths
+      // with a trailing directory separator.
+      return rtrim($directory, DIRECTORY_SEPARATOR);
     }
   }
   return FALSE;