Update manpages for r250887.

Remove the lists of unneeded header files.

Requested by:	eadler
Add proper prerequisites for even two more headers.

Spotted by:   http://hacks.owlfolio.org/header-survey/
passing fd over unix socket: fix a corner case where caller
wants to pass no descriptors.

Previously the kernel would leak memory and try to free a potentially
arbitrary pointer.

Reviewed by:	pjd