Datetime support

[gabor]

At the risk of being accused of feature creep I silently added support
for datetime support in the optimizer (you need to attach it
manually:

require("RedBean/Plugin/Optimizer.php");
$optimizer = new RedBean_Plugin_Optimizer( $toolbox );
$redbean->addEventListener("update", $optimizer);

).

The Optimizer will now convert columns with datetime values to
datetimefields. If a different value is inserted the column will be
reverted by OODB in fluid mode.

As you may know the optimizer acts silently and in the background.

Warning: The optimizer does not check (yet) for fluid/frozen mode so
only attach this in fluid mode!

[gabor]

only released to github for now.