pgsql: Provide moving-aggregate support for a bunch of numerical aggreg

Provide moving-aggregate support for a bunch of numerical aggregates.

First installment of the promised moving-aggregate support in built-in
aggregates: count(), sum(), avg(), stddev() and variance() for
assorted datatypes, though not for float4/float8.

In passing, remove a 2001-vintage kluge in interval_accum(): interval
array elements have been properly aligned since around 2003, but
nobody remembered to take out this workaround. Also, fix a thinko
in the opr_sanity tests for moving-aggregate catalog entries.

David Rowley and Florian Pflug, reviewed by Dean Rasheed

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9d229f399e87d2ae7132c2e8feef317ce1479728

Modified Files
--------------
src/backend/utils/adt/int8.c | 63 +++-
src/backend/utils/adt/numeric.c | 379 +++++++++++++++++++++---
src/backend/utils/adt/timestamp.c | 72 +++--
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_aggregate.h | 266 ++++++++---------
src/include/catalog/pg_proc.h | 20 ++
src/include/utils/builtins.h | 7 +
src/include/utils/int8.h | 2 +
src/include/utils/timestamp.h | 1 +
src/test/regress/expected/opr_sanity.out | 12 +-
src/test/regress/expected/window.out | 475 ++++++++++++++++++++++++++++++
src/test/regress/sql/opr_sanity.sql | 12 +-
src/test/regress/sql/window.sql | 141 +++++++++
13 files changed, 1230 insertions(+), 222 deletions(-)