remove ndat member, #4

src/@dates/append.m

src/@dates/colon.m

src/@dates/copy.m

src/@dates/dates.m

src/@dates/end.m

src/@dates/eq.m

src/@dates/ge.m

src/@dates/gt.m

src/@dates/horzcat.m

src/@dates/intersect.m

src/@dates/isempty.m

src/@dates/isequal.m

src/@dates/le.m

src/@dates/length.m

src/@dates/lt.m

src/@dates/max.m

src/@dates/min.m

src/@dates/minus.m

src/@dates/mtimes.m

src/@dates/ndat.m