Add a strtoul() wrapper

src/common.c

@@ -1417,6 +1417,15 @@ set_boolean_if_valid (bool *out, const char *s)
 	return true;
 }
 
+static bool
+xstrtoul (unsigned long *out, const char *s, int base)
+{
+	char *end;
+	errno = 0;
+	*out = strtoul (s, &end, base);
+	return errno == 0 && !*end && end != s;
+}
+
 static bool
 read_line (FILE *fp, struct str *s)
 {