Futex error handling

[Roland McGrath]

> We got complains from the kernel side that glibc wouldn't react properly
> to futex errors being returned.  Thus, I'm looking at what we'd need to
> actually improve.  I'm using this here as a documentation for futex
> error codes: https://lkml.org/lkml/2014/5/15/356

Can somebody work with Michael et al to ensure that the futex(2) man page
becomes reliable documentation for this?