Improved aqbanking and gwenhywfar

When updating the devel builds for the aqbanking and gwenhywfar formulae I noticed, that they did not pick up the keg-only gettext properly, furthermore the updated sources for devel introduce new dependencies,
figuring out how to satisfy those nicely was quite the PITA.

While working on the formulae I changed some depends_on and option defaults, which from my point of view make more sense.

I've experimented with various ways of how to do the install in order to support the current and the devel build,
and have tested the proposed changes thoroughly in various combinations.

I welcome and encourage any feedback on what could be improved or be done differently.