set pconnect false by default

From Zend:

Please note that using persistent connections can cause an excess of
idle connections on the RDBMS server, which causes more problems than
any performance gain you might achieve by reducing the overhead of
making connections.

Database connections have state. That is, some objects in the RDBMS
server exist in session scope. Examples are locks, user variables,
temporary tables, and information about the most recently executed
query, such as rows affected, and last generated id value. If you use
persistent connections, your application could access invalid or
privileged data that were created in a previous PHP request.