Support Amazon Redshift

[ansgarbecker]

Various SQL modifications required for supporting Redshift.

Feature discussion takes place on https://www.heidisql.com/forum.php?t=34635 - here's the ticket.

Relevant commits so far:

• 7eb486f
• 3bcfbfd (actually for Column comments are not visible #62)

Documentation on Redshift:

• https://docs.aws.amazon.com/redshift/latest/dg/c_redshift-and-postgres-sql.html
• https://www.postgresql.org/docs/8.0/release-8-0-2.html

[ansgarbecker]

• Status bar should say we're on "Amazon Redshift" instead of just PostgreSQL. Example result of SELECT VERSION() from dburtsev:
  PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.10936