Patch: Add --no-comments to skip COMMENTs with pg_dump

Hi,

Attached is a patch adds a --no-comments argument to pg_dump to skip
generation of COMMENT statements when generating a backup. This is crucial
for non-superusers to restore a database backup in a Single Transaction.
Currently, this requires one to remove COMMENTs via scripts, which is
inelegant at best.

A similar discussion had taken place earlier [1], however that stopped
(with a Todo entry) since it required more work at the backend.

This patch provides a stop-gap solution until then. If the feedback is to
tackle this is by filtering comments for specific DB objects, an argument
name (for e.g. --no-extension-comments or something) would help and I could
submit a revised patch.

Alternatively, if there are no objections, I could submit this to the
Commitfest.

References:
[1] https://www.postgresql.org/message-id/1420.1397099637%40sss.pgh.pa.us

-
robins
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