Do not call connect() for each executed query

[wouter bolsterlee]

AnewtDatabasePreparedQuery::executev() calls AnewtDatabaseConnection::connect(), which calls AnewtDatabaseConnection::is_connected(). This results in needless database roundtrips and hence a performance penalty for (at least) MySQL connections, since the is_connected() call results in a MySQL::ping() call.

A better approach is described here:
http://www.mysqlperformanceblog.com/2010/05/05/checking-for-a-live-database-connection-considered-harmful/

[wouter bolsterlee (wbolster)]

 1789 Wouter Bolsterlee 2010-10-02
      [database] Don't try to connect before each query

      Avoid checking for a valid connection for each executed
      query. It adds extra server roundtrips for at least the
      MySQL backends and does not work reliably anyway.

      This also means that disconnected connections do not
      automatically try to (re)connect anymore, but relying on
      this was bad practice and couldn't possibly work reliably
      with transactions anyway.