co-installable qt4-mac and qt5-mac step1 : qt4-mac +concurrent

[René J.V. Bertin]

'evening!

I finally got around to finishing up (or almost) my draft version for a qt4-mac port that can live alongside other (future) Qt port versions installed with the same approach: see https://trac.macports.org/ticket/46238 .

Related submissions:
https://trac.macports.org/ticket/46239
https://trac.macports.org/ticket/46240

Hope this helps! :)

René