pgsql: dshash: Make it possible to suppress out of memory errors

dshash: Make it possible to suppress out of memory errors

Introduce dshash_find_or_insert_extended, which is just like
dshash_find_or_insert except that it takes a flags argument.
Currently, the only supported flag is DSHASH_INSERT_NO_OOM, but
I have chosen to use an integer rather than a boolean in case we
end up with more flags in the future.

Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: http://postgr.es/m/CA+TgmoaJwUukUZGu7_yL74oMTQQz2=zqucMhF9+9xBmSC5us1w@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6f0738ddec85b416e7186e3099be70a3420bf3ea

Modified Files
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src/backend/lib/dshash.c | 94 +++++++++++++++++++++++++++++++++++-------------
src/include/lib/dshash.h | 12 +++++--
2 files changed, 79 insertions(+), 27 deletions(-)