added support for ILIKE and NOT ILIKE operators

[brendanstennett]

Sometimes Vertica complains about UPPER(str) LIKE UPPER('%str%') when comparing longer strings. Vertica does however support ILIKE just like PostgreSQL and does not complain when comparing longer strings.

This PR adds support for ILIKE and NOT ILIKE

[brendanstennett]

Travis failed but it looks like it was actually a test setup problem for 1.9.3 and nothing to do with running the tests at all.

Also note that this implementation is taken directly out of sequel itself in the way that this is implemented for PostgreSQL.

https://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/shared/postgres.rb#L1253

[camilo]

LGTM but conflicts with another patch

[brendanstennett]

Rebased.