Request: hash check for Main before replacing

[birdybro]

No other core would really require this, but a hash check for the main would help. I have helped others a good handful of times with their Main getting corrupted upon update, and the screen is black upon restart. This has also happened to me a few times (but I'm a bit of a power user and I redo my mister install and download main updates frequently. When this happens they have to replace the file with a new one from the site. It only occurs when there is an update. It might be a little complex, but I think there is good reason to treat Main a little differently for stability reasons and users ability to control the system.