Add support for InnoDB full-text search indexes

[3manuek]

innodb_space does not support yet InnoDB FTS indexes.

emanuel@3laptop ~/sandboxes/rcsandbox_mysql-5_7_9/node1/data/test $ innodb_space -I test/oe_email -T test/Emails  -s ../ibdata1 index-recurse
/var/lib/gems/1.9.1/gems/innodb_ruby-0.9.13/lib/innodb/system.rb:213:in `index_by_name': undefined method `[]' for nil:NilClass (NoMethodError)
    from /var/lib/gems/1.9.1/gems/innodb_ruby-0.9.13/bin/innodb_space:1730:in `<top (required)>'
    from /usr/local/bin/innodb_space:23:in `load'
    from /usr/local/bin/innodb_space:23:in `<main>'

Thanks for such great tool! :D