Summary: PHP Strict Standards define that you can't declare static methods
abstract, so I just commented out __xhpAttributeDeclaration declaration like
__toString() should not throw "Exception"s, but trigger_error() is accepted, so I
just catch any Exception and trigger an E_USER_ERROR using the exception's
There's almost no trade off as you probably don't handle exceptions when you
convert XHP objects to string. If you have some kind of global error handling
you should make sure that the Exception handling and error handling should have
the same behaviour.