gdImageScaleTwoPass memory leak fix

Fixing memory leak in gdImageScaleTwoPass, as reported by @cmb69 and
confirmed by @vapier.  This bug actually bit me in production and I'm
very thankful that it was reported with an easy fix.

Fixes #173.
static double KernelBessel_P1(const double x)
{
	double p, q;

	register long i;

	static const double
	Pone[] =
	{
		0.352246649133679798341724373e+5,
		0.62758845247161281269005675e+5,
		0.313539631109159574238669888e+5,
		0.49854832060594338434500455e+4,
		0.2111529182853962382105718e+3,
		0.12571716929145341558495e+1
	},
	Qone[] =
	{
		0.352246649133679798068390431e+5,
		0.626943469593560511888833731e+5,
		0.312404063819041039923015703e+5,
		0.4930396490181088979386097e+4,
		0.2030775189134759322293574e+3,
		0.1e+1
	};

	p = Pone[5];
	q = Qone[5];
	for (i=4; i >= 0; i--)
	{
		p = p*(8.0/x)*(8.0/x)+Pone[i];
		q = q*(8.0/x)*(8.0/x)+Qone[i];
	}
	return (double)(p/q);
}

static double KernelBessel_P1(const double x)
{
	double p, q;

	register long i;

	static const double
	Pone[] =
	{
		0.352246649133679798341724373e+5,
		0.62758845247161281269005675e+5,
		0.313539631109159574238669888e+5,
		0.49854832060594338434500455e+4,
		0.2111529182853962382105718e+3,
		0.12571716929145341558495e+1
	},
	Qone[] =
	{
		0.352246649133679798068390431e+5,
		0.626943469593560511888833731e+5,
		0.312404063819041039923015703e+5,
		0.4930396490181088979386097e+4,
		0.2030775189134759322293574e+3,
		0.1e+1
	};

	p = Pone[5];
	q = Qone[5];
	for (i=4; i >= 0; i--)
	{
		p = p*(8.0/x)*(8.0/x)+Pone[i];
		q = q*(8.0/x)*(8.0/x)+Qone[i];
	}
	return (double)(p/q);
}
