Description:
------------
In case an optional parameter is followed by NOT optional parameter, reflection 
behaves incorrectly.

On that particular instance of ReflectionParameter, isDefaultValueAvailable() 
returns TRUE but getDefaultValue then throws.



I tested it on 5.3.11 where it worked (but where it threw away the default 
value), on 5.3.16 it throws.

Test script:
---------------
class Foo {
	function bar($a = NULL, $b) { }
}

$rm = new ReflectionMethod('Foo', 'bar');
foreach ($rm->getParameters() as $param) {
	echo $param->getName(), "\n";
	var_dump($param->isDefaultValueAvailable());

	if ($param->isDefaultValueAvailable()) var_dump($param->getDefaultValue());
}

Expected result:
----------------
a
bool(true)
NULL
b
bool(false)

Actual result:
--------------
// on 5.3.16
a
bool(true)

Fatal error: Uncaught exception 'ReflectionException' with message 'Parameter is 
not optional'



// on 5.3.11
a
bool(false)
b
bool(false)