pushed https://hg.savannah.gnu.org/hgweb/octave/rev/803e6fc006ed to default.  patch changes the default from mean to median.  it adds an optional mode input that allows the user to select median or mean. the option is stripped from varargin before passing the call to movfun, with fcn being either "@mad" or "@(x) mad (x, 1)". adds tests, doc notes, news note.

So this makes the code compatible, ands an extension to let octave continue calling a moving mean absolute deviation which matlab doesn't have. it's been 8 years, but if they add it later, this method of enabling the selection should be adaptable to whatever they later do.

marking as ready for test.