[Nmh-workers] Major POSIX push to master

[Ken Hornstein]

Greetings all,

I've just pushed to master all of the relevant changes that I've cherry-picked
from Lyndon Nerenberg's posix branch (other than Makefile changes, the only
ones I didn't do was one creating definitions for NI_MAXHOST and NI_MAXSERV
since we're not compiling strict POSIX, and one assuming that we never had
d_type in struct dirent; there is an autoconf test for that, and I think that's
worth the performance gain).

I checked and things compiled okay for me.  With this work we got rid of
a lot of autoconf tests and dusty old #ifdefs.  Thanks to Lyndon for
all of the hard work he did in making this happen!

--Ken