Re: Add new COPY option REJECT_LIMIT

Hi! Nice feature.

Few comments:

> +      When a positive integer value is specified, <command>COPY</command> limits
> +      the maximum tolerable number of errors while converting a column's input
> +      value into its data type.

If nothing is specified, then the maximum tolerable number of errors
is one, right? Should we state  this explicitly in the documentation?

> +COPY x from stdin with (on_error ignore, reject_limit 0);
How about a test where reject_limit is a string, but not
(case-intensively) 'infinity'?

> + CopyRejectLimits reject_limits; /* thresholds of reject_limit */

Why are there multiple thresholds? Can we have only one?

Other places look good to me.