Bug in database handling for postgres

[bobtfish]

Took me a while of tracing through the application to work this one out.. The function which has a problem is 'insert_id' in program/include/rcube_db.inc

For postgresql, no value is returned from the switch statement, which implicitly falls through, runs the query 'SELECT @@IDENTITY' which generates an exception, and then returns this exception..

This causes a row in the 'identity' table to not be created when a user is created and you are using the 'virtuser_query' config setting.

Trivial patch to fix attached.

[bobtfish]

Fix a bug in the handling of postgres databases.

[thomasb]

Fixed in Trunk (r504)