pgsql: tidbitmap: Support shared iteration.

tidbitmap: Support shared iteration.

When a shared iterator is used, each call to tbm_shared_iterate()
returns a result that has not yet been returned to any process
attached to the shared iterator. In other words, each cooperating
processes gets a disjoint subset of the full result set, but all
results are returned exactly once.

This is infrastructure for parallel bitmap heap scan.

Dilip Kumar. The larger patch set of which this is a part has been
reviewed and tested by (at least) Andres Freund, Amit Khandekar,
Tushar Ahuja, Rafia Sabih, Haribabu Kommi, and Thomas Munro.

Discussion: http://postgr.es/m/CAFiTN-uc4=0WxRGfCzs-xfkMYcSEWUC-Fon6thkJGjkh9i=13A@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/98e6e89040a0534ca26914c66cae9dd49ef62ad9

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 6 +-
src/backend/access/gin/ginget.c | 2 +-
src/backend/executor/nodeBitmapIndexscan.c | 2 +-
src/backend/executor/nodeBitmapOr.c | 2 +-
src/backend/nodes/tidbitmap.c | 551 +++++++++++++++++++++++++++--
src/backend/storage/lmgr/lwlock.c | 1 +
src/include/nodes/tidbitmap.h | 10 +-
src/include/storage/lwlock.h | 1 +
8 files changed, 536 insertions(+), 39 deletions(-)