Replaced funtion atan(omega1 / Delta_omega) with atan2(omega1 , Delta_omega), to make sure returned theta values are between 0 and pi.
This was done in the function return_offset_data() in the specific_analyses of relax_disp.
This was discussed in: http://thread.gmane.org/gmane.science.nmr.relax.devel/5210.
