pgsql: Add pg_depend.refobjversion.

Add pg_depend.refobjversion.

Provide a place for the version of referenced database objects to be
recorded.  A follow-up commit will use this to record dependencies on
collation versions for indexes, but similar ideas for other kinds of
objects have also been mooted.

Author: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Discussion: https://postgr.es/m/CAEepm%3D0uEQCpfq_%2BLYFBdArCe4Ot98t1aR4eYiYTe%3DyavQygiQ%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/cd6f479e79f3a33ef7a919c6b6c0c498c790f154

Modified Files
--------------
doc/src/sgml/catalogs.sgml                | 11 +++++++++++
src/backend/catalog/dependency.c          | 14 ++++++++++----
src/backend/catalog/pg_depend.c           | 14 ++++++++++----
src/include/catalog/catversion.h          |  2 +-
src/include/catalog/dependency.h          |  1 +
src/include/catalog/pg_depend.h           |  4 ++++
src/include/catalog/toasting.h            |  1 +
src/test/regress/expected/misc_sanity.out |  4 ++--
8 files changed, 40 insertions(+), 11 deletions(-)