always respect OnlyShowIn and NotShowIn

[otommod]

From reading the spec, I think the current behavior is wrong. If one really needs to be able to execute everything, even DE-specific entries, an option could be added but I don't think anybody would want that.

I also made several other changes, I don't know if you want them in a different PR or even at all.

[jceb]

Thanks a lot. Please separate the commits into a number of prs.

[otommod]

I rebased and kept only the relevant commits here.

[jceb]

Thanks a lot!