bug#3746: M-r in comint mode should use isearch

[Juri Linkov]

>> Please see the attached code that implements isearch in comint mode.
>
> What would be the "UI" (e.g. key-binding) for it?
> Only the comint-history-isearch defcustom?

One way to use this feature is to configure `comint-history-isearch' to
a non-nil value.  But I think it should be nil by default because after
trying to use it with non-nil values I found it counterintuitive since
in comint mode on typing `C-r' I expect it to search in the comint output,
not in the input history.

There is no such problem in bash where C-r searches in the input history,
since there is no way to search in the bash output.

So we need another key to search in the history.  However, this is
a controversial issue, so I will defer to others to decide what key
to use for that.  (In the code I sent, there is a command
`comint-history-isearch-backward' that could be bound to any key.)

-- 
Juri Linkov
http://www.jurta.org/emacs/