libpq: PQgetCopyData() and allocation overhead

Would there be interest in a variant of PQgetCopyData() that re-uses the
same buffer for a new row, rather than allocating a new buffer on each
iteration?

I tried it on a toy benchmark, and it reduced client-side CPU time by about
12%. (Less of a difference in wall-clock time of course; the client was
only using the CPU for a bit over half the time.)

Jeroen