bug#66700: 30.0.50; Some history is missing with multiple eshell buffers

[Liu Hui]

Hi,

Eshell saves history by default when quitting the buffer or emacs, but
some history is missing when there are multiple eshell buffers. For
example,

1. emacs -Q
2. M-x eshell, and type foo
3. C-u M-x eshell, and type bar
4. quit emacs

I would expect both commands are saved, but in fact only one command
is saved in the file eshell-history-file-name. I think the reason is
the history file is always overwritten when an eshell buffer tries to
save the history, so maybe eshell should save commands by appending
to the file?

Best

--
Liu Hui