% Determine sqw type from the data component of an sqw data structure
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%   >> type = sqw_type(data)
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%   data        data componenet of sqw structure
%   type        ='b','b+' 'a' (valid sqw type) or 'a-' (sqw without pix)
%               ='h' if header part of data structure only
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%   Simple routine - the assumption is that the data corresponds to a valid type
%   Needs full data structure, not just the header fields
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