ErrorHandler::stackErrors()

Configures the error handler for delayed handling.

Ensures also that non-catchable fatal errors are never silenced.

As shown by http://bugs.php.net/42098 and http://bugs.php.net/60724 PHP has a compile stage where it behaves unusually. To workaround it, we plug an error handler that only stacks errors for later.

The most important feature of this is to prevent autoloading until unstackErrors() is called.