pmc: release the message cache on exit.

This makes valgrind happier by freeing any cached message buffers.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

pmc.c

@@ -830,5 +830,6 @@ int main(int argc, char *argv[])
 	}
 
 	pmc_destroy(pmc);
+	msg_cleanup();
 	return 0;
 }