Re: extend pgbench expressions with functions

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make installcheck-world: tested, passed
Implements feature: tested, passed
Spec compliant: tested, passed
Documentation: tested, passed

Hello.

I installed centos 6.7 version on virtualbax, have cloned postgres from GitHub.
And then i patched to postgres as the patch file with the following command:
$ patch -p1 < pgbench-expr-abs-9.patch

To make sure that the patch apply to postgres, i wrote two script files.
The script file is:
$ cat before.sql
\set naccounts 100000 * :scale
\setrandom aid 1 :naccounts
$ cat after.sql
\set aid random(1, 100000 * :scale)

Using the script file in pgbench, i run :
$ ./pgbench -T 3 -P 1 -f before.sql
$ ./pgbench -T 3 -P 1 -f after.sql

This was run well. I test for the functions(e.g abs, ddebug, double, exporand, idebug, int, gaussrand, min, max, random, sqrt) mentioned in the patch, it was also executed without error.

Finally i reviewed code in patch, but did not find to error.