Better Error Message on Date/Time functionality

[hakre]

Currently Wordpress does warn that something does not work with Date/Time in admin when using a PHP version < 5.2.

From a usability standpoint it would be useful to extend the error message with the concrete technical cause of the error so that admins do not need to get themselves educated any further prior to just fixing the issue.

Suggested fix would be to add some more info to the error message, like the needed PHP version: "You need at least PHP version 5.2 to have this feature enabled.". Currently that information is missing.

[hakre]

​As reported, upgrading to PHP 5.2 does remove the error message.

Related: #9751

[nacin]

This string will be gone in 3.2.