[enh] display engine error messages

searx/search.py

                              .format(engine_name, search_duration, timeout_limit, e))
             requests_exception = True
         else:
-            result_container.add_unresponsive_engine((engine_name, gettext('unexpected crash')))
+            result_container.add_unresponsive_engine((
+                engine_name,
+                u'{0}: {1}'.format(gettext('unexpected crash'), e),
+            ))
             # others errors
             logger.exception('engine {0} : exception : {1}'.format(engine_name, e))