bug#10885: Replace expressions: enhance functionality when searching in filled paragraphs

[Juri Linkov]

>> Since query-replace is going in the direction of closer integration with
>> isearch, the right thing would be to get its search function from isearch.
>
> Agreed.

Installed.  Since this enhancement request is completely implemented,
and all mentioned problems are fixed, I'm closing it.

>>  (defun replace-highlight (match-beg match-end range-beg range-end
>> -                      string regexp case-fold)
>> +                      string regexp word case-fold)
>
> Maybe we should use an isearch-state argument?

Actually these arguments correspond to the variables of `perform-replace',
not isearch state.  So I renamed them to the names used in `perform-replace',
causing isearch-related let-bindings in `replace-highlight' to be
the exact copy of let-bindings in `perform-replace'.