[Nmh-workers] 8-bit, 8bit; 7-bit, 7bit

[Larry Hynes]

I'm aware that mhfixmsg takes 8bit and 7bit flags, but I'm not sure
that should mean the man page text should refer to 8bit throughout,
as in let the flag be 7bit, but lets refer to 7-bit.

(somewhat) Similarly, mhbuild refers to 7-bit, and 8bit. I've
settled, for now unless told otherwise, on n-bit in mhbuild, and
would like to do the same in mhfixmsg, when it's referring to a
flag.