Allow (S)EP with arbitrary sequence of innovations.

The third input argument of extended_path Matlab/Octave's routine is the
sequence of shocks (T*n array, where n is the number of exogenous
variables and T is the size of the sample). If the third argument is
empty, the (stochastic) extended path is run with gaussian
innovations (this corresponds to the previous behaviour).

TODO:
 - Fix the compatibility with ep.replic_nbr
 - Check the 'calibrated' mode.

ComputingTasks.cc

@@ -3200,7 +3200,7 @@ ExtendedPathStatement::writeOutput(ostream &output, const string &basename, bool
       output << "options_." << it->first << " = " << it->second << ";" << endl;
 
   output << "extended_path([], " << options_list.num_options.find("periods")->second
-         << ", options_, M_, oo_);" << endl;
+         << ", [], options_, M_, oo_);" << endl;
 }
 
 ModelDiagnosticsStatement::ModelDiagnosticsStatement()