pgsql: Ensure an index that uses a whole-row Var still depends on its t

Ensure an index that uses a whole-row Var still depends on its table.

We failed to record any dependency on the underlying table for an index
declared like "create index i on t (foo(t.*))".  This would create trouble
if the table were dropped without previously dropping the index.  To fix,
simplify some overly-cute code in index_create(), accepting the possibility
that sometimes the whole-table dependency will be redundant.  Also document
this hazard in dependency.c.  Per report from Kevin Grittner.

In passing, prevent a core dump in pg_get_indexdef() if the index's table
can't be found.  I came across this while experimenting with Kevin's
example.  Not sure it's a real issue when the catalogs aren't corrupt, but
might as well be cautious.

Back-patch to all supported versions.

Branch
------
REL8_2_STABLE

Details
-------
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=6b1952b07176723b98d8ca0ce3d913bf1360c8af

Modified Files
--------------
src/backend/catalog/dependency.c  |   15 ++++++++++++++-
src/backend/catalog/index.c       |   15 +++++----------
src/backend/utils/adt/ruleutils.c |   24 +++++++++++++++++++++---
3 files changed, 40 insertions(+), 14 deletions(-)