Version Check/Required Ambiguity

This is something that I will open an issue with but I thought I would discuss it here first, to see what people think.

At the moment the version check for addons is:

version_compare($NewVersion, $Version, '>')

this is ok but it is limited in a way, it always assumes that it is compatible with future versions.

You can actually put additional logic in setup, but it would be good if could be integrated.

I will be doing a lot of development into the future and I want to be flexible, especially as I will be developing quite atomically.

I can think of a number of scenarios:

1. One version only, exact match, stop gap solution perhaps.
2. Quite often you see stuff like this >=2.0.18 it would be useful if it could detect those operators an plug into into the function since it has that capability to be exact.
3. in other cases you need an range you could have for instance >=2.0.17,<=2.0.18

Another scenario that I personally faced was I wanted to require one plugin or another. Actually EXOR. I think it fair that I put my own logic in the setup, which I did. However I think it would be good to give some clue in the Requirements. Perhaps a way to put a requirement that is ignored.

I suppose you could always unset the key, before it gets checked. All scenarios have hacks, but might as well make it sleek.