This PR begs a question:

	should every system call manual page list every possible
	error that can be returned by that call?

For example, this means that any system call dealing with a 
descriptor (file, socket, whatever) would need to list all filesystem 
error codes, plus all socket (network) error codes, and so on. It 
would be a fairly exhaustive list.

If we decide "yes" then we need to go through section 2 pretty thoroughly.

The alternative is to list the error codes in one place, and give a 
general description of when to expect them, with pointers to the 
right subset from each system call man page.

Or we could just say UTSL with a pointer to /usr/include/errno.h

	comments?

	Erik <fair@clock.org>