Description:
------------
Actually there is a difference between read and include authorization: I can't read a file, but, at the same time, I can include it (read about safe_mode_include_dir).
Unfortunately there is no way to check if I can include a file or not.
Actually the only way to do this is perform an include, and this is not always what we want to do.

Reproduce code:
---------------
function check_plugins($pluginsFromConfig) {
  foreach($pluginsFromConfig As $filepath) {
    if(is_includable($filepath)===false) {
      trigger_error('plugin not found',E_USER_ERROR);
      exit;
    }
    else echo 'plugin -bla- -bla- exists';
  }
}

Expected result:
----------------
We expect to know if a file can be included, without include it.

Actual result:
--------------
Function is_includable doesn't exist. We tried to use file_exists, etc. but are limited by safe_mode restrictions.
Documentation say that we can use is_readable for ignore safe_mode restriction but it doesn't work and if it will work it will be logically wrong.