fixed catsting to (int)e in serial error messages.

see https://github.com/ErikZalm/Marlin/issues/148

Marlin/temperature.cpp

   disable_heater();
   if(IsStopped() == false) {
     SERIAL_ERROR_START;
-    SERIAL_ERRORLN(e);
+    SERIAL_ERRORLN((int)e);
     SERIAL_ERRORLNPGM(": Extruder switched off. MAXTEMP triggered !");
   }
 }
   disable_heater();
   if(IsStopped() == false) {
     SERIAL_ERROR_START;
-    SERIAL_ERRORLN(e);
+    SERIAL_ERRORLN((int)e);
     SERIAL_ERRORLNPGM(": Extruder switched off. MINTEMP triggered !");
   }
 }