`Mining_Drones_Harder` fails to load due to stray folder in archive

[redruin1]

Attempting to load Mining_Drones_Harder_1.0.0 will fail due to a stray folder titled __MACOSX in the rootmost directory level. I assume this is leftover from some version conversion script.

The wiki is (as usual) unclear as to exactly why this is permitted, since it implies that it's not, yet Factorio loads it just fine. Instead, I'm taking a guess that will hopefully be right:

• If there is only one folder in the archive, use that;
• If there is multiple folders in the archive, we use the folder that matches the zipfile name exactly;
• Otherwise, throw an IncorrectModFormatError.

It might also have to do with the folder name being prepended by underscores (or this particular folder name is reserved on OSX as it seems to indicate) but until I can get more information on it this will be the functionality in version 1.0.3.