fix most sign and variable initialization warnings

Change-Id: I56e08db791152a9c95fc0d16bc75b702e403274d
diff --git a/include/libbb.h b/include/libbb.h
index 8b09f5a..a38ecf2 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1465,9 +1465,9 @@
 	int flags;
 	const char *path_lookup;
 # if MAX_HISTORY
-	int cnt_history;
-	int cur_history;
-	int max_history; /* must never be <= 0 */
+	unsigned cnt_history;
+	unsigned cur_history;
+	unsigned max_history; /* must never be <= 0 */
 #  if ENABLE_FEATURE_EDITING_SAVEHISTORY
 	/* meaning of this field depends on FEATURE_EDITING_SAVE_ON_EXIT:
 	 * if !FEATURE_EDITING_SAVE_ON_EXIT: "how many lines are