struct_vect2singleton: detect another type of conversion error

Signed-off-by: Mark Histed <mhisted@gmail.com>
some frm_ updates as I transition to matlab's dataset

Signed-off-by: Mark Histed <mhisted@gmail.com>
structincell2cellarray: use legacy setdiff, I haven't looked into what's changed in new setdiff to know what the introduced bug is

Signed-off-by: Mark Histed <mhisted@gmail.com>