Description:
------------
ReflectionParameter::isOptional() does not return the correct optional status of some parameters.

ReflectionFunction::getNumberOfRequiredParameters() returns the current number of required parameters, but when iterator through the ReflectionFunction::getParamaters() counting parameters that are not marked as optional, the value calculated is incorrect.


Reproduce code:
---------------
class TestClass
{
}
function optionalTest(TestClass $a, TestClass $b, $c = 3)
{
}

$function = new ReflectionFunction('optionalTest'); 
$numberOfNotOptionalParameters = 0;
$numberOfOptionalParameters = 0;
foreach($function->getParameters() as $parameter)
	if ($parameter->isOptional())
		++$numberOfOptionalParameters;
	else
		++$numberOfNotOptionalParameters;
var_dump($function->getNumberOfRequiredParameters());
var_dump($numberOfNotOptionalParameters);

Expected result:
----------------
int(2) int(2) 

Actual result:
--------------
int(2) int(0)