bug#13923: 24.3.50; doc strings of Isearch commands

[Juri Linkov]

> The doc strings of `isearch-forward' etc. should describe each of the
> arguments.  That includes arg NO-RECURSIVE-EDIT.  This applies to all
> Isearch commands.

The docstring of `isearch-forward' describes the whole Isearch facility
for interactive use with all its available commands and keys.

There is only one place to describe `isearch-forward' as a non-interactive
function at the end of the docstring that already contains this text:

    If this function is called non-interactively, it does not return to
    the calling function until the search is done.

that describes the effect of NO-RECURSIVE-EDIT.

> The doc string of `isearch-mode', especially, needs to describe each of
> its arguments.  It currently describes none of them.

This is described already in the Commentary section of isearch.el:

  ;; For programmed use of isearch-mode, e.g. calling (isearch-forward),
  ;; isearch-mode behaves modally and does not return until the search
  ;; is completed.  It uses a recursive-edit to behave this way.

and in the comments of `isearch-mode':

  ;; isearch-mode can be made modal (in the sense of not returning to
  ;; the calling function until searching is completed) by entering
  ;; a recursive-edit and exiting it when done isearching.