Post WP3.1 PHP 5 register_shutdown_function() note - Remove Backwards compability

[hakre]

In some classes (DB, Cache) register_shutdown_function() is used to mimic destruct() in PHP 4 so it looks appropriate to remove that when wordpress codebase becomes PHP 5.2+.

But in fact the register_shutdown_function() probably must be kept for backwards compatibility, bećause desctruct() is not called in PHP 5.2+ in all cases in which register_shutdown_function() registered functions are called.

So to remove the shutdown hook will break backwards compatibility because it is buggy for a mimic of destruct().

I suggest to remove this buggy implementation and break with backwards compatibility.

[Denis-de-Bernardy]

These were introduced because of #3354 and similar issues. Which affect 5.2 platforms...

Suggesting wontfix until we require PHP 5.3 or PHP 6.