Description:
------------
When setting your own custom error handler and then calling an undefined function then the error handler isn't triggered.

I read on the manual that:
"If errors occur before the script is executed (e.g. on file uploads) the custom error handler cannot be called since it is not registered at that time."

But I would expect undefined function errors to be apart of the execution as a function might be created dynamiclly.

I also found bug '#11803' and read that fatal errors aren't passed to custom error handler functions, but It would be nice to be able to fetch such errors in larger applications.


Cheers

Reproduce code:
---------------
<?php
	function error_handler($errno, $errstr, $errfile = NULL, $errline = NULL, $errcontext = NULL)
	{
		var_dump($errno, $errstr, $errfile, $errline);

		return(true);
	}

	set_error_handler('error_handler');

	undef_function();

	/** Rest of the script */
?>

Expected result:
----------------
int(2)
string(28) "Call to undefined function undef_function()"
string(29) "/webserver/webroot/test.php"
int(11)

Actual result:
--------------
Fatal error: Call to undefined function undef_function() in /webserver/webroot/test.php on line 11