:auto-increment support for primary keys MySQL only

Hey there,

it looks as if the support for auto-increment in CL-SQL is currently a
MySQL-ism. I.e., the code in update-records-from-instance has a
hard-coded "SELECT LAST_INSERT_ID()" in it, whereas for Postgres
(which is what I'm using) needs a CURRVAL('serial_variable') (see
https://secure.wikimedia.org/wikibooks/en/wiki/Converting_MySQL_to_PostgreSQL#Functions).

So the select should probably move to a backend specific method. I'll
see if I can come up with a patch in the next days.

Holger