% Read the detector parameter from a binary file.
%
% Syntax:
%   >> [det, mess] = get_sqw_detpar(fid, det_in)
%
% Input:
% ------
%   fid         File pointer to (already open) binary fil
%
% Output:
% -------
%   det         Structure containing fields read from file (details below)
%   mess        Error message; blank if no errors, non-blank otherwise
%
% Fields read from file are:
%   det.filename    Name of file excluding path
%   det.filepath    Path to file including terminating file separator
%   det.group       Row vector of detector group number
%   det.x2          Row vector of secondary flightpath (m)
%   det.phi         Row vector of scattering angles (deg)
%   det.azim        Row vector of azimuthal angles (deg)
%                  (West bank=0 deg, North bank=90 deg etc.)
%   det.width       Row vector of detector widths (m)
%   det.height      Row vector of detector heights (m)
%
%