bug#22479: 25.0.50; isearch and query-replace histories do not remember if we were looking for symbols

[Juri Linkov]

>> 5. More ideas? ;)
>
> - We can retain the two histories: regex, non-regex
>
> - Any fancy (word, symbol, etc) searches can be stored into the regex
>   history, bookmarked with the appropriate regexen ("\_<", "\_>" for
>   instance)
>
> - When reading the history to present to the user, these can be parsed
>   out. So for instance when the user looks through the symbol-search
>   history by hitting
>
>   M-s _
>   C-s
>
>   emacs can look through the regex history, only selecting entries in
>   \_<...\_>. The C-M-s history can either include all of these, or show
>   only unbookmarked entries; both would be ok, I think.

This approach is compromising but unreliable (doesn't distinguish
between the case when the user uses the symbol search M-s _
or types \_<...\_> directly in the regexp search) and insufficient
(need to remember other search parameters like case-fold and lax-whitespace).