The filename argument to which() may already be absolute

For example $Config{make} may contain "/usr/bin/make" and not just "make".
Remove dead code checking for $quote

If the $dir entry contained quotes, then File::Spec->catfile($dir, $name)
ends up with quotes in the middle of the name.  Either way, the -x check
will not return true for such a name, so this check doesn't make any sense.
Merge #224