Re #10805 Modify solid angle correction for tubes

The instrument scientists asked to modify the solid angle correction for tubes.
The code they sent was the following:

    if (is_tube)
    {
    	tanAlpha = tan( getYTubeAngle(det, inputWS) );
		tanTheta = tan( inputWS->detectorTwoTheta(det) );		
		const double term1 = sqrt(tanAlpha*tanAlpha + 1.0);
		const double term2 = sqrt(tanTheta*tanTheta + 1.0);
		const double corr = term1*term2*term2;
    } else {
        tanTheta = tan( inputWS->detectorTwoTheta(det) );
		const double term3 = sqrt(tanTheta*tanTheta + 1.0);
		const double corr = term3*term3*term3;
    }

Please double check the implementation. The system tests should all pass and there should be no change in functionality.