Re: More macro dispatching

[Akim Demaille]

In order to properly implement the proposal of Alexandre (expr=false
when we can't trust it), more responsibility should be moved into
Mash, in particular things like _AC_INIT_PREPARE_ENVIRONMENT.  It is a
good thing, it is independent from Autoconf and useful to any Mash
project (understand `autoscript' or `autosh' here).

But to be really clean, some form of AC_REQUIRE would be good too.
This time, it is not related to sh in any way, so I'm proposing to
move AC_REQUIRE, AC_DEFUN and company into m4sugar.  Again, I think
this is a good thing, some other projects than Autoconf might want it.
It'd be m4_defun, m4_require etc.

Alexandre and Lars think it's a good thing to do.  They emphasized it
should be done for any other macro which interest is not limited to
Autoconf.

Would someone have a different opinion?