pgsql: Make pg_relation_size() and friends return NULL if the object do

Make pg_relation_size() and friends return NULL if the object doesn't exist.

That avoids errors when the functions are used in queries like "SELECT
pg_relation_size(oid) FROM pg_class", and a table is dropped concurrently.

Phil Sorber

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/fa352d662e57fa150158b9cb0a8f127250f8c97f

Modified Files
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doc/src/sgml/func.sgml         |    5 ++
src/backend/utils/adt/dbsize.c |  119 ++++++++++++++++++++++++++++------------
2 files changed, 89 insertions(+), 35 deletions(-)