Solaris recently introduced the idea of drive topology because
where a drive is located does matter. I have already handled
this with udev/blkid integration under Linux so I'm hopeful
this case can simply be removed but for now I've just stubbed
out what is needed in libspl and commented out the rest here.
All but the pthreads changes have been committed upstream and in
the name of keeping the topgit tree as simple as possible I'm removing
the entire 'feature' subtree. The pthreads changes are now a 'fix'.
Brian Behlendorf