this was exposed in #313 by @vitorgalvao in his attempt to update the
anvil cask; by adding a link to that cask, (which just so happens to be
the cask that we chose for our "already uninstalled message" test).
the fix is simply to move the "already uninstalled" check *before* we
start to unlink.
homebrew does internal caching in ARGV that prevents us from doing the
`ARGV.clear; ARGV << 'newarg'` trick twice.
rather than try to further reach in to homebrew's innards, i figure it's
better to just pass multiple arguments down to homebrew code at once,
since it already supports that
refs #47
this delegates to homebrew's uninstall to get its work done. vanilla
`brew uninstall` actually works, but this gives us a more consistent
interface.
as discussed in #47
Paul Hinze
phinze