Resolving compatibility issues with MySQL COMMENT:

- Removing backticks from `COMMENT` option in `CREATE TABLE` syntax in order to remain compatible with older versions of MySQL which seem to choke on backticks inside single-quote encapsulation.

- Removing COMMENT syntax from all index definitions in order to remain compatible with MySQL v5.1.

See: https://github.com/websharks/comment-mail/issues/74