pgsql: Disallow LATERAL references to the target table of an UPDATE/DEL

Disallow LATERAL references to the target table of an UPDATE/DELETE.

On second thought, commit 0c051c90082da0b7e5bcaf9aabcbd4f361137cdc was
over-hasty: rather than allowing this case, we ought to reject it for now.
That leaves the field clear for a future feature that allows the target
table to be re-specified in the FROM (or USING) clause, which will enable
left-joining the target table to something else.  We can then also allow
LATERAL references to such an explicitly re-specified target table.
But allowing them right now will create ambiguities or worse for such a
feature, and it isn't something we documented 9.3 as supporting.

While at it, add a convenience subroutine to avoid having several copies
of the ereport for disalllowed-LATERAL-reference cases.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/158b7fa6a34006bdc70b515e14e120d3e896589b

Modified Files
--------------
src/backend/parser/analyze.c        |   12 ++++---
src/backend/parser/parse_relation.c |   62 +++++++++++++++++++++--------------
src/include/parser/parse_node.h     |    3 +-
src/test/regress/expected/join.out  |   48 +++++++++++----------------
src/test/regress/sql/join.sql       |   13 ++++----
5 files changed, 72 insertions(+), 66 deletions(-)