Reorganized the way we deal with functions which exist under only some versions of MATLAB and/or some versions of Octave:
* Created a directory matlab/missing to store them under subdirectories
* Add the needed subdirectories to the path from dynare_config.m
* Moved content of matlab/matlab/ and matlab/octave/ to matlab/missing/*/
* matlab/missing/ordeig/ordeig.m: new name of matlab/my_ordeig
* matlab/missing/ordschur/ordschur.m: fake replacement, displays an error message
* Removed old matlab/matlab/ and matlab/octave/ directories


git-svn-id: https://www.dynare.org/svn/dynare/trunk@2805 ac1d8469-bf42-47a9-8791-bf33cf982152