Provide 32 and 64 bit Octave mex-files
As indicated at http://savannah.gnu.org/bugs/index.php?49289, there will be a 64 bit version of Octave 4.2, which then also will allow to use the 64bit Dynare preprocessor (see #1306 (closed)). This will hopefully also solve #1304 (closed). But this means we need to provide 64bit mex-files as well as the 32bit ones do not run.