Missing important use case in documentation for module_load_include()

Re-rolled since last one failed to apply.

Seems a good idea to include the reporter's comment in code.
I'm putting it to RTBC because as i've seen it works well and can be merged.

Given that the function has the word "module" in its name, and especially given that it contains the following code:

   $file = DRUPAL_ROOT . '/' . drupal_get_path('module', $module) . "/$name.$type";

It seems pretty clear to me that a NULL $module only works by accident, no? I don't think it's an intended use of this function.

Usually Drupal loads files from the includes directory via a direct require, like this:

    require_once DRUPAL_ROOT . '/includes/common.inc';

With module-provided files, the module_load_include() API exists because a module can be installed at a variety of different places within the site's directory structure, and the API allows the calling code to not have to know where the file is located in order to include it.

But the core includes directory always exists in the same place... so files can just be directly loaded from it.