Description:
------------
A bundle named "supplementalData" can't be read by ResourceBundle. If the bundle 
is named "supplementaldata" instead, loading works.

To reproduce, create a supplementalData.txt with this content:

--- BEGIN ---
supplementalData{
}
--- END ---

Then run genrb on the CLI:

$ genrb supplementalData.txt

which will generate a supplementalData.res needed by the test. genrb will output 
a warning, but you can ignore that for the purpose of this test.

Test script:
---------------
<?php
$bundle = new \ResourceBundle('supplementalData', __DIR__);
var_dump($bundle instanceof \ResourceBundle);

Expected result:
----------------
bool(true)

Actual result:
--------------
bool(false)