New function normal_rand_array function to contrib/tablefunc.

Here is a new function which could produce an array of numbers with a
controllable array length and duplicated elements in these arrays. I
used it when working with gin index, and I think it would be helpful for
others as well, so here it is.

select * from normal_rand_array(5, 10, 1.8::numeric, 3.5::numeric);
normal_rand_array
-----------------------------------------------
{3.3,2.3,2.7,3.2,2.0,2.7,3.4,2.7,2.3,2.9}
{3.3,1.8,2.9,3.4,2.0,1.8,2.0,3.5,2.8,2.5}
{2.1,1.9,2.3,1.9,2.5,2.7,2.4,2.9,1.8}
{2.3,2.5,2.4,2.7,2.7,2.3,2.9,3.3,3.3,1.9,3.5}
{2.8,3.4,2.7,1.8,3.3,2.3,2.2,3.5,2.6,2.5}
(5 rows)

select * from normal_rand_array(5, 10, 1.8::int4, 3.5::int4);
normal_rand_array
-------------------------------------
{3,2,2,3,4,2}
{2,4,2,3,3,3,3,2,2,3,3,2,3,2}
{2,4,3}
{4,2,3,4,2,4,2,2,3,4,3,3,2,4,4,2,3}
{4,3,3,4,3,3,4,2,4}
(5 rows)

the 5 means it needs to produce 5 rows in total and the 10 is the
average array length, and 1.8 is the minvalue for the random function
and 3.5 is the maxvalue.

--
Best Regards
Andy Fan