Reset oo_.{exo_}steady_state to zero before endval

This is necessary to enforce the documented behavior which says that, if a
variable is not given a value in the endval block, a zero value is assumed.

preprocessor/NumericalInitialization.cc

 /*
- * Copyright (C) 2003-2012 Dynare Team
+ * Copyright (C) 2003-2013 Dynare Team
  *
  * This file is part of Dynare.
  *
@@ -245,7 +245,9 @@ EndValStatement::writeOutput(ostream &output, const string &basename) const
          << "%" << endl;
   // Writing endval block to set terminal values for variables
   output << "ys0_= oo_.steady_state;" << endl
-         << "ex0_ = oo_.exo_steady_state;" << endl;
+         << "ex0_ = oo_.exo_steady_state;" << endl
+         << "oo_.steady_state = zeros(size(ys0_));" << endl
+         << "oo_.exo_steady_state = zeros(size(ex0_));" << endl;
 
   writeInitValues(output);
 }