#1 kludge "port" & "unix_socket" args; fix MySQL null handling

[Chris Waterson]

This patch is sort of a kludge to add "port" and "unix_socket"
parameters to the simplesql-open routine. It's not backward
compatible, since it inserts the parameters in the optional list
"where they ought to go". A real solution would probably have
some sort of string parsed here a la Perl's DBI or something, but
feh.

Also included is a patch that fixes null handling for MySQL.
Specifically, don't treat "len == 0" as null; instead, rely on
row[pos] == 0 when the value is null.

[Chris Waterson]

Patch, diff -ur