Incorrect format in error message

The attached fixes an error message which is incorrectly using an
unsigned format specifier instead of a signed one.

# create table t ();
# create unique index t_idx on t (ctid);
# alter table t replica identity using index t_idx;
ERROR: internal column 4294967295 in unique index "t_idx"

I was just going to submit a patch to change the %u to a %d, but this
error message should use ereport() instead of elog(), so I fixed that
up too and added the missing regression test.

I picked ERRCODE_INVALID_COLUMN_REFERENCE as I thought it was the most
suitable. I'm not sure if it's correct though.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services