pgsql: Provide real selectivity estimators for inet/cidr operators.

Provide real selectivity estimators for inet/cidr operators.

This patch fills in the formerly-stub networksel() and networkjoinsel()
estimation functions. Those are used for << <<= >> >>= and && operators
on inet/cidr types. The estimation is not perfect, certainly, because
we rely on the existing statistics collected for the inet btree operators.
But it's a long way better than nothing, and it's not clear that asking
ANALYZE to collect separate stats for these operators would be a win.

Emre Hasegeli, with reviews from Dilip Kumar and Heikki Linnakangas,
and some further hacking by me

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/89840d7d3fa943cb932f6a00707fdb17a9cab001

Modified Files
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src/backend/utils/adt/network_selfuncs.c | 980 +++++++++++++++++++++++++++++-
1 file changed, 977 insertions(+), 3 deletions(-)