Make Pg::Explain understand Index Only Scans

For certain nodes Pg::Explain can extract table/index/column names. This
is helpful for anonymization.
This wasn't done (the extraction) for Index Only Scans.
Fixed extraction, anonymization works correctly (and other things that
depend on list of tables extracted from plan), like Stats on
http://explain.depesz.com/
fix manifest after adding new test file
Apparently using perl -T & perlbrew gives warnings

I think it's a problem with Test::Harness, but removing -T seemed like an
easy option.
Fix for Perl::Critic

3-argument open was added in 5.6, so ther should be version requirement.
PerlCritic rule is overreaching

This rule causes problems when dealing with hashrefs like this:
$hashref->{ 'key' }
I could theoretically add object layer around the hashes, but it doesn't
make sense. Removing the critic rule seems saner.
Release 0.67