pgsql: Create AVG() aggregates for int8 and NUMERIC which do not compute

Log Message:
-----------
Create AVG() aggregates for int8 and NUMERIC which do not compute X^2,
as a performance enhancement.

Mark Kirkwood

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        numeric.c (r1.99 -> r1.100)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/numeric.c.diff?r1=1.99&r2=1.100)
    pgsql/src/include/catalog:
        catversion.h (r1.385 -> r1.386)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.385&r2=1.386)
        pg_aggregate.h (r1.60 -> r1.61)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_aggregate.h.diff?r1=1.60&r2=1.61)
        pg_proc.h (r1.444 -> r1.445)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.444&r2=1.445)
    pgsql/src/include/utils:
        builtins.h (r1.287 -> r1.288)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h.diff?r1=1.287&r2=1.288)
    pgsql/src/test/regress/expected:
        create_aggregate.out (r1.5 -> r1.6)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_aggregate.out.diff?r1=1.5&r2=1.6)
    pgsql/src/test/regress/sql:
        create_aggregate.sql (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/create_aggregate.sql.diff?r1=1.6&r2=1.7)