pgsql: Use 128-bit math to accelerate some aggregation functions.

Use 128-bit math to accelerate some aggregation functions.

On platforms where we support 128bit integers, use them to implement
faster transition functions for sum(int8), avg(int8),
var_*(int2/int4),stdev_*(int2/int4). Where not supported continue to use
numeric as a transition type.

In some synthetic benchmarks this has been shown to provide significant
speedups.

Bumps catversion.

Discussion: 544BB5F1.50709@proxel.se
Author: Andreas Karlsson
Reviewed-By: Peter Geoghegan, Petr Jelinek, Andres Freund,
    Oskari Saarenmaa, David Rowley

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/959277a4f579da5243968c750069570a58e92b38

Modified Files
--------------
src/backend/utils/adt/numeric.c    |  428 ++++++++++++++++++++++++++++++++----
src/include/catalog/catversion.h   |    2 +-
src/include/catalog/pg_aggregate.h |  102 ++++-----
src/include/catalog/pg_proc.h      |   15 ++
src/include/utils/builtins.h       |    7 +
5 files changed, 463 insertions(+), 91 deletions(-)