[HACKERS] Small patch for pg_basebackup argument parsing

Hi

Yesterday while doing a few pg_basebackup, I realized that the integer
parameters were not properly checked against invalid input.
It is not a critical issue, but this could be misleading for an user who
writes -z max or -s 0.5…
I've attached the patch to this mail. Should I add it to the next commit fest
or is it not needed for such small patches ?

Thanks

 Pierre