Coerce a relatively simple object to an RMINC known object
(currently mincList, mincSingleDim, mincMultiDim)
Value
if x is a known minc type return it, if it is a list, attempt
to reduce it toa minc object via simplify2minc, otherwise check
if the object has columns, if so reclass it as mincMultiDim otherwise
reclass it as a mincSingleDim