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
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6b387179baab8d0e5da6570678eefbe61f3acc79

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(-)