Description:
------------
If you pass a GMP resource as parameter to gmp_fact(), it calculates and returns the factorial of the internal resource number, not of the GMP value in the resource.

In the PHP manual the function prototype is given as:
    "resource gmp_fact ( int $a )"
However, in the parameter description it says:
    "It can be either a GMP number resource,
    or a numeric string given that it is possible
    to convert the latter to a number."

This is misleading.

Furthermore gmp_fact should check the parameter type and either accept GMP resources or throw a warning.

Reproduce code:
---------------
<?php

for ($i = 0; $i < 3; $i++) {
        $nine = gmp_init('9');
        var_dump($nine);
        echo '9! = ',   gmp_strval(gmp_fact($nine)),   "\n";
}


Expected result:
----------------
resource(4) of type (GMP integer)
9! = 362880
resource(6) of type (GMP integer)
9! = 362880
resource(8) of type (GMP integer)
9! = 362880

*** or ***

resource(4) of type (GMP integer)
9! = 
Warning: gmp_fact(): parameter must be int
resource(6) of type (GMP integer)
9! = 
Warning: gmp_fact(): parameter must be int
resource(8) of type (GMP integer)
9! = 
Warning: gmp_fact(): parameter must be int

Actual result:
--------------
resource(4) of type (GMP integer)
9! = 24
resource(6) of type (GMP integer)
9! = 720
resource(8) of type (GMP integer)
9! = 40320