Report error position in partition bound check

Hi,

I'm playing with partitioned tables and found a minor thing with the
error reporting of bounds checking when create partitions.

In function check_new_partition_bound(), there are three places where
we call ereport() with a parser_errposition(pstate, spec->location)
argument. However, that pstate is a dummy ParseState made from NULL,
so the error message never reports the position of the error in the
source query line.

I have attached a patch to pass in a ParseState to
check_new_partition_bound() to enable the reporting of the error
position. Below is what the error message looks like before and after
applying the patch.

-- Create parent table
create table foo (a int, b date) partition by range (b);

-- Before:
create table foo_part_1 partition of foo for values from (date
'2007-01-01') to (date '2006-01-01');
ERROR: empty range bound specified for partition "foo_part_1"
DETAIL: Specified lower bound ('2007-01-01') is greater than or equal to
upper bound ('2006-01-01').

-- After:
create table foo_part_1 partition of foo for values from (date
'2007-01-01') to (date '2006-01-01');
ERROR: empty range bound specified for partition "foo_part_1"
LINE 1: ...eate table foo_part_1 partition of foo for values from (date...
^
DETAIL: Specified lower bound ('2007-01-01') is greater than or equal to
upper bound ('2006-01-01').

Another option is to not pass the parser_errposition() argument at all
to ereport() in this function, since the query is relatively short and
the error message is already descriptive enough.

Alex and Ashwin