Fix compiler warnings in auth-token stuff.

auth_token/linux/internal.h

@@ -31,6 +31,7 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <string.h>
+#include <ctype.h>
 #include <syslog.h>
 #include <errno.h>
 #include <pthread.h>