pgsql: Fix misc typos, mostly in comments.

Fix misc typos, mostly in comments.

A collection of typos I happened to spot while reading code, as well as
grepping for common mistakes.

Backpatch to all supported versions, as applicable, to avoid conflicts
when backporting other commits in the future.

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/65976cd86a9bdeec5a5277545e5efa33724102c8

Modified Files
--------------
contrib/bloom/blscan.c                    |  2 +-
doc/src/sgml/protocol.sgml                |  2 +-
doc/src/sgml/spi.sgml                     |  2 +-
src/backend/access/transam/multixact.c    |  4 ++--
src/backend/commands/cluster.c            |  2 +-
src/backend/commands/explain.c            |  2 +-
src/backend/executor/nodeModifyTable.c    |  2 +-
src/backend/optimizer/plan/planner.c      |  4 ++--
src/backend/parser/parse_func.c           |  2 +-
src/backend/replication/logical/origin.c  |  2 +-
src/backend/utils/time/snapmgr.c          |  4 ++--
src/bin/initdb/t/001_initdb.pl            |  2 +-
src/bin/pg_upgrade/tablespace.c           |  2 +-
src/include/nodes/execnodes.h             |  2 +-
src/include/nodes/parsenodes.h            | 10 +++++-----
src/include/port/pg_bswap.h               |  2 +-
src/include/storage/latch.h               |  2 +-
src/include/utils/rel.h                   |  2 +-
src/interfaces/ecpg/ecpglib/execute.c     |  4 ++--
src/interfaces/ecpg/preproc/parse.pl      |  4 ++--
src/pl/tcl/pltcl.c                        |  2 +-
src/test/regress/expected/rowsecurity.out |  2 +-
src/test/regress/expected/rules.out       |  2 +-
src/test/regress/sql/rowsecurity.sql      |  2 +-
src/test/regress/sql/rules.sql            |  2 +-
25 files changed, 34 insertions(+), 34 deletions(-)