Remove a couple of comments from the pg_lsn regression test.

Previously, one of these was a negative test case, but that got
changed along the way and the comments didn't get the memo.

Michael Paquier
Use pg_lsn data type in pg_stat_replication, too.

Michael Paquier, per a suggestion from Andres Freund
docs: document behavior of CHAR() comparisons with chars < space

Space trimming rather than space-padding causes unusual behavior, which
might not be standards-compliant.

Also remove recently-added now-redundant C comment.
Allow single-point polygons to be converted to circles

This allows finding the center of a single-point polygon and converting
it to a point.

Per report from Josef Grahn
Fix markup for CHAR() doc patch
pg_dump:  fix subtle memory leak in func and arg signature processing
psql:  add separate \d display for disabled system triggers

Previously if you disabled all triggers, only user triggers would
show as disabled

Per report from Andres Freund
docs:  remove unnecessary references to old PG versions
Increase work_mem and maintenance_work_mem defaults by 4x

New defaults are 4MB and 64MB.
Update and clarify ssl_ciphers default

- Write HIGH:MEDIUM instead of DEFAULT:!LOW:!EXP for clarity.
- Order 3DES last to work around inappropriate OpenSSL default.
- Remove !MD5 and @STRENGTH, because they are irrelevant.
- Add clarifying documentation.

Effectively, the new default is almost the same as the old one, but it
is arguably easier to understand and modify.

Author: Marko Kreen <markokr@gmail.com>