changes denominator FRC calcualtion

Brian Patton, University of Strathclyde, Glasgow
says that the original computation for the numerator was wrong, namely:
numerator[i] = dataA1[i] * dataA2[i] + dataB1[i] * dataB2[i];

And should be instead:
abs((FFT(Image1)*Complex_Conj(FFT(Image2)))