Allow loading perl5i::2 twice in the same namespace without warning.

[schwern]

If you load perl5i::2 twice in the same namespace, you'll get warnings.

use perl5i::2;
use perl5i::2;

Subroutine main::CLASS redefined at /Users/schwern/perl5/perlbrew/perls/perl-5.16.2-threads/lib/site_perl/5.16.2/CLASS.pm line 20.
Prototype mismatch: sub main::open (*;$@) vs none at /Users/schwern/perl5/perlbrew/perls/perl-5.16.2-threads/lib/site_perl/5.16.2/perl5i/2/UNIVERSAL.pm line 23.

Eliminate those warnings. The first one is a fairly straightforward double export. CLASS.pm doesn't use Exporter. Best to fix that in CLASS.pm.

$ perl -wle 'use CLASS; use CLASS'
Subroutine main::CLASS redefined at /Users/schwern/perl5/perlbrew/perls/perl-5.16.2-threads/lib/site_perl/5.16.2/CLASS.pm line 20.

The second is part of the interaction between use utf8::all and use autodie both want open.

Originally reported in #250.