[Nmh-workers] mh-e support in nmh

[Ken Hornstein]

So I've been looking at removing crud in nmh's autoconf support and mass
of #ifdefs, and I came across the --enable-mhe option.

This defines MHE during the build, and it enables a few bits of MHE
support (some commands get a -build switch, and inc does some extra stuff).

The default has been to build with mh-e support, and I suspect that very
few people have NOT built nmh with mh-e support so I doubt that it is
causing many problems.  I propose removing the configure option and associated
#ifdefs so that mh-e support is always included in nmh.  Comments?

--Ken