How can I tell if module_load_include() is working?
module_load_include() returns FALSE if it can't find the file, and the full path to the file included if it can find the file, and it was successfully included. In addition to that, it uses require_once which will throw a fatal E_COMPILE_ERROR error if the file is not found.

An easy way to debug would be to use code like this in your loop:

$file_path = module_load_include($type, $module, $filename);

if ($file_path === FALSE) {
  dpm('Failed to include: ' . $filename);
}
else {
  dpm('Successfully included: ' . $file_path);
}


That will give you a pretty solid answer as to whether or not the files are being included. If you get no debug messages, you know that the glob() isn't returning the list of files that it should be.