Honor --sbindir and --bindir for binary installation
Some distros don't care about the split between /bin, /sbin, /usr/bin,
and /usr/sbin, so let them easily stuff binaries wherever they want.
This also fixes a problem during installation where-in a loop of 'chmod
4755' calls will mostly fail. However, because the last two succeed
(newuidmap/newgidmap), make considers the command to be a success.
Somewhat not-amusingly, configuring shadow with --with-fcaps will cause
installation to fail because the final chmod call is now a failing one.