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_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/ed529faf7ec1e1a879c6f3b9eecd426c813749e6

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/executor/nodeModifyTable.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/parsenodes.h            | 10 +++++-----
src/include/storage/latch.h               |  2 +-
src/interfaces/ecpg/ecpglib/execute.c     |  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 +-
18 files changed, 25 insertions(+), 25 deletions(-)