Runtime Config Option for identifier case preservation

Attached is a patch to allow the user to change the behavior of postgres with
reguards to case sensitivity on unquoted identifiers. This does not change
the default behavior of converting unquoted identifiers to lowercase, but
does allow (for instance, and I'm absolutly -not- pulling from personal
experience here <g>) a large project to run under postgres that did run under
MySQL a whole bunch easier.

for example, these two SQL statements sets are identical
set parser-ignore-case = false;
select "Address_id" from "Address";

set parser-ignore-case = true;
select Address_id from Address;