port "cask" -- installing prebuilt binaries

[Ken Cunningham]

So this issue seems still active, but without a decided plan here, people are just starting to PR their favourite approach, which is of course exactly what we are tring to avoid. 

The idea of identifying them by a variant suffers from the fact that these are obviously not variants, they are immutable downloaded binaries without a non-prebuilt version. So that is just confusing. 

There are very rare ports like ghc where a downloaded binary rebuilds the macports version. In that rare case only, a prebuilt variant sorta makes some sense, but our previous naming scheme where we called it "ghc-bootstrap" was probably more appropriate, TBH.

Chris says put them in a category. Logical, but I don't know if most users would note that when trying to install them, as it is not perhaps obvious enough these are different beasts.

Really obvious is to tag a small suffix on the name, which nobody could ever miss. Then everyone will know immediately what they are dealing with, including those of us who resolve tickets. That's why I like that idea.

So lets get some decision, whatever it is, before we have to clean up a big mess as people Bogart ahead with different plans.

Ken