Setup proposal: "Maintainer Features" #define and AC_ARG_ENABLE

[Max Bowsher]

I'd like to resubmit my 'alternative registry name' patch for setup. It's
not something that should go into released versions, but is the kind of
thing that a maintainer is likely to find useful. I'd like to have a new
#define (say MAINTAINER_FEATURES) and AC_ARG_ENABLE
(say --enable-maintainer-features) for things that a maintainer could
compile into their normal everyday setup, and activate on the command line
as required (as distinct from DEBUG, which is for stuff that causes
extremely verbose logging, or is otherwise undesirable for an everyday
binary).

Comments?

Max.