shell: update HISTFILESIZE code to be actually useful

"HISTFILESIZE=0" in profile wasn't working as intended,
"unset HISTFILE" wasn't preventing creation of history files
Now:
HISTSIZE=n      allows to reduce in-memory history buffer
HISTFILESIZE=n  allows to reduce history file size (0: truncate it)
unset HISTFILE  allows to not save history file at all

function                                             old     new   delta
exitshell                                            138     194     +56
hush_exit                                             97     143     +46
save_history                                         266     296     +30
hush_main                                           1170    1186     +16
.rodata                                           105762  105771      +9
load_history                                         246     254      +8
size_from_HISTFILESIZE                                44      41      -3
read_line_input                                     2746    2712     -34
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 6/2 up/down: 165/-37)           Total: 128 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 801f072fa..e765e18eb 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1989,7 +1989,7 @@ typedef struct line_input_t {
 # if MAX_HISTORY
         int cnt_history;
         int cur_history;
-        int max_history; /* must never be <= 0 */
+        int 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