Octave unit tests. Add io package.

tests/runalltests.m

@@ -13,6 +13,10 @@
 % You should have received a copy of the GNU General Public License
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
+if isoctave()
+    pkg install -forge io
+end
+
 opath = path();
 
 system('rm -f failed');