Covering the comparison between date and timestamp, tz, type

Hi,

Using the PostgreSQL code coverage report, I found that tests for
comparisons between date and timestamp[tz] are missing. Some of them have
only partial coverage.

Attached patch will cover following functions:

date_eq_timestamp
date_ne_timestamp
date_lt_timestamp
date_gt_timestamp // already covered
date_le_timestamp
date_ge_timestamp

date_eq_timestamptz
date_ne_timestamptz
date_lt_timestamptz // already covered
date_gt_timestamptz // already covered
date_le_timestamptz
date_ge_timestamptz

timestamp_eq_date
timestamp_ne_date
timestamp_lt_date
timestamp_gt_date // already covered
timestamp_le_date
timestamp_ge_date

timestamptz_eq_date
timestamptz_ne_date
timestamptz_lt_date
timestamptz_gt_date // already covered
timestamptz_le_date
timestamptz_ge_date // already covered

This is a minor patch, but I’d like to submit it to enhance test coverage.

Best regards,
Kwangwon Seo