Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22268, verified by myself.

Add definitions for weak aliases so that libhack functions
are actually linked instead of libc ones on ELF systems.
Fixes install/13050 and install/13153.

fix warning allegedly reported on i386

Prune out references to qsort in opendir unionfs code.
(Never needed on a ramdisk root.)