'Fix' the export.sh

It seems to be working this way, at least.

Not sure that's the best way to get rid of the old (external local::lib) PERL5LIB, or if local::lib=--deactivate-all should be taking care of it... but it works!
Added the `die` because installer.pm's fatpacked version of CPAN::Perl::Releases was too old to contain 5.18.2. This at least makes it a nicer error.