Fix overflow in parsing of positional parameter

Fix overflow in parsing of positional parameter

Replace atol with pg_strtoint32_safe in the backend parser and with
strtoint in ECPG to reject overflows when parsing the number of a
positional parameter.  With atol from glibc, parameters $2147483648 and
$4294967297 turn into $-2147483648 and $1, respectively.

Author: Erik Wienhold <ewie@ewie.name>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: http://www.postgresql.org/message-id/flat/5d216d1c-91f6-4cbe-95e2-b4cbd930520c@ewie.name