replace 'struct array2d' with 'class array2d' for consistency
replace 'struct array2d' with 'class array2d' for consistency

Reported by Bart Kevelham

cusplibrary/cusplibrary,cusplibrary/cusplibrary,sdalton1/cusplibrary,sdalton1/cusplibrary,sdalton1/cusplibrary,sdalton1/cusplibrary,cusplibrary/cusplibrary,cusplibrary/cusplibrary