[PATCH v2] Remove union wait

[Roland McGrath]

> Oh.  I wasn't aware that 4.3+BSD was a term made up by Richard Stevens
> for the 1993 edition of Advanced Programming in the UNIX Environment
> (which predates 4.4BSD).

The last book I read about Unix programming was the first edition of K&R
(unless you count the hardcopy set of of 4.3BSD man pages I had).  I only
refer to the sources, header files, and machine-readable documentation
that's part of the system.

> In any case, union wait is not documented at all in the book.

An example of why such books are not good resources for authoritative
information.

> > This should probably be more thoroughly rewritten, probably dropping the
> > section and describing wait3 as obsolete just alongside wait4.
> 
> That's a separate patch, right?

Either way, as long as it doesn't get forgotten and doesn't lag long past
the code patch.  The state your patch leaves the manual in looks a bit like
the state source code gets in after a patch that removes a bunch of code
but doesn't remove comments that refer to that code.